Thunderbolt speed problems.

the Cables required for top Thunderbolt speeds to drives or displays must be certified ThunderBolt cables that carry the ThunderBolt symbol, and be appropriately SHORT. For top speeds, that means no longer than 0.8 meters for Apple cables, 0.5 meters for brand X cables.

Wwe do see reported speeds for the internal drives in Mac studio approaching 5,000 M Bytes/sec WRITES and 3,500 M Bytes/sec Reads on a quick test, such as the one built into Etrecheck.

This result is almost 'backward' from expected measurements. This is likely due to a large built-in Write buffer on the drive, which makes writes appear faster on a short-duration test.

FYI, I have a 1TB WD SN850 in my Acasis TB enclosure and runs 2500+ speeds and also a 1TB WD SN750 in a Trebleet TB enclosure that runs about the same 2500 speeds. You are correct that a RAID configuration should run almost double the speed so the 5000 may be correct.

What you say is quite correct as far as it goes.

The problem is that once the data are pulled off the fast RAID set, the ThunderBolt "Pipe" used to transfer the data to the Mac has limited bandwidth. which clips the top transfer speeds.

This may be why both measurements could be correct -- under certain conditions.

I question your measurement of 5,000 M Bytes a sec on any Mac except in an internal slot in a Mac Pro.

ThunderBolt-3 or 4 Macs can get up to nominal 2500 M Bytes/sec on an appropriately fast SSD drive in a ThunderBolt-3 enclosure, provided they use a non-busy ThunderBolt controller on the Mac (not shared controller busy servicing displays or other drives on a second Mac port) supported by a typical 32 G bits/sec (PCIe2 x4, or PCIe3 x2 amount of bandwidth). 

Iin the case of M-series Macs, one ThunderBolt port is generally serviced by one ThunderBolt controller, so there is no other traffic competing.

Yes, this is a problem with the Mac Studio that I've personally experienced.

If you run a hardware diagnostic from the recovery/boot menu it will also tell you there is an issue which apple support told me was related to PCI bus width. If you disconnect one of the external thunderbolt enclosures the error goes away.

The workaround that I found for (my) problem is to use powered thunderbolt hubs.

You don't need four hubs. If you're using four external thunderbolt drives you only need one hub. Connect two of the drives to the hub and the other two directly to the rear I/O. Bam, speed is full on all external drives and everything works. The Mac also says all four drives are connected over PCI-E, so it's not using USB on the hub.

I think the problem is the Mac Studio cannot supply enough power for that many devices so the powered hub helps. Your mileage may very, I don't use the acasis drives but do use another brand. You may need more powered hubs than I have depending on your machine and setup.

Edit: Correction, I have three drives connected directly to the thunderbolt ports and the fourth is on my thunderbolt hub. So I'm getting full speed. But if you connect two drives to the hub the speed of those two drives will be halved in a raid array setup.