Q: New Mac; the local hard drive is too small for my requirements

Typical flash storage won't fit in the new Mac Pro. As you can see here, it looks much more like a USB flash drive:

Flash storage you normally buy are the SSD design, which look like a flat hard drive:

If you look up PCIe Flash Storage, they're all designed like a standard PCI card you plug into an open slot.

Apple has a page showing how to remove the current flash stick and put in a new (presumably, larger one).

As of this time, the only place I can find selling direct upgrades is Other World Computing. As you can see, they're far from cheap. Though when compared to one of the very few 2 TB SSD drives you can find, $1500 for a 2 TB PCIe flash card sounds pretty good.

So that answers your first two questions. Yes, you can change the current configuration, and yes, you can order one. The only change would be swapping out the chips, then booting into Internet Recovery Mode so you can set up the new drive with Disk Utility and install OS X.

You'll have to contact OWC to get a quote for the full cost of selling and shipping one of these drives to South Africa.

Blade SSDs can be found on ebay.

The ones from OWC are slower and not a good idea, well you could use them but probably in EXTERNAL Thunderbolt.

The Samsung XP941 and later, but not M.2 design.

You can find a lot of discussion here:

SATA Express meets the '09 MacPro - Bootable NGFF PCIE SSD  (  1 2 3 4 5 6 ... Last Page)

If you clone the system there is no reason to use Internet Recovery.

I didn't read through the entire discussion you linked to, but from what I saw, everyone was linking to PCI slot plug-in cards, none of which will fit into a cylinder Mac Pro.

Putting "Blade SSD" into Amazon'a search shows me nothing but adapters you can plug into the Mac Pro's PCIe slot in order to use the cheaper, but slower SSD chips. Did I miss any actual PCIe cards? I also checked on the Samsung chips, and neither those, or any other brand had anything larger than 512 GB. I would presume those wouldn't be any larger than what the OP is trying to replace.

I did find this nifty Thunderbolt enclosure, though. You could leave the chip currently in the Mac Pro alone and add the storage externally.

Hatter, are you talking about these OWC blades being slow?

http://www.macrumors.com/2014/12/09/owc-ssd-upgrades-2013-mac-pro/

I was wondering that, too (same link I have above). Apple's main pretty page on the Mac Pro states the storage data rate at as high as 1200 MB/s. If the stock storage sticks really run that fast, then that is quite a bit higher than OWC's stick, rated by them at 726 MB/s. However, I can't find anywhere on Apple's site that states how fast their storage actually runs. Everything else simply says 256 GB SSD standard, upgradable to 512GB or 1 TB. No mention at all of data rate.

Edit: Ah! Here's one. Apple's stock SSD sticks are quite a bit faster, averaging just about right at 1000 MB/s.

The Internal SSD on the cylinder Mac Pro may meet the requirements of a few isolated Users, but it is actually intended as the Boot Drive (only) and User data is intended to be located on External Drives, such as ThunderBolt arrays or a limited number of USB-3 attached drives.

USB-3 drives are comparatively affordable, but there is a tragic flaw. The Mac Pro bandwidth dedicated to all the USB-3 Busses is equivalent to one Bus device at its full possible speed, Reading and Writing simultaneously.

This means that once you have more than one device Reading AND One device Writing simultaneously, you may see speed reductions from the theoretical maximum speeds. In many cases, especially with Rotating drives and ordinary workflows, this may not make a substantial difference with a handful of drives. But Video Editors should not even consider USB-3 options for their Video.

With Balck Magic my 512 GB drive gets 718 write/846 read with 1 GB data

One user who posted information about the black metal heatsink over the "blade" SSD in the Mac Pro showed that the underside of that flat metal heatsink has heat-conductive tape placed to transfer heat from the large chips to the metal heatsink.

Users should use caution in replacing these "blade" drives to maintain appropriate heat dissipation with a similar heatsink and carefully-placed heatsink tape over the big components.

Don't know if the OWC chip has a heat sink on the back for contact with the thermal core, but their page does show sinks attached to the front of the chip for dissipation.

However, you are quite right that the supplied storage is really only meant for booting and space for your installed apps. Beyond that, your larger storage needs should be Thunderbolt arrays. Even with a large number of large apps installed on my current 2010 Mac Pro, I only have 40 GB used of my boot partition. So even the basic 256 GB drive would be plenty big enough.

I do not think the Apple black SSD heatsink (shown in your photo above) touches the thermal core or even the X-shaped pressure retainer you can see in the photo.

I expect when Apple engineers actually got the parts (which were faster than anything else on the market) they found them running surprising HOT, and decided it needed something, however primitive that might be. So I think that heatsink was very much an afterthought.

It is reassuring to see the OWC parts with an applied heatsink as well.

The photo of the open Mac Pro is just from Apple's page about the product. I presume the picture is of their installed storage stick in place. No idea what's on the back side of it. Some sort of heat sink on the underside as Grant mentioned, I would presume.

This thread:

Re: Black plate on SSD important?

Then scroll down and simrix has posted four pictures in a row of the black plate. Three of four shows the inside with the heatsink tape in place in the correct positions to pick up the heat from the Big Chips on the SSD.

[bloody forum software].

Thanks! So there's a couple of pieces of thermal tape which are positioned to contact the two chips in the storage stick, which transfer the heat the chips produce to the back plate, which is in direct contact with the thermal core.