Firstly there is a near identical question about setup of just days ago that hopefully you found and looked at in your research.
System on SSD / scratch for CS6 / projects
Lloyd's blog is full of tips: http://www.macperformanceguide.com
Start with what SSD (single) then get into multiple and setup and apps and how they are used, which really might be first thing to ask?
The Pro uses highest quality but both have much of the same controller and firmware - and it was just reviewed as to what the diference is. Find and read that.
Rick over on MacGurus setup an old working model for PS: a scratch disk + working project files is the fastest - was done with SCSI and then the first 10K SATA Raptor. Probably still holds true.
No you are not limited - I strongly suggest you set it up on Sonnet Tempo Pro RAID card and then use one 250GB 840 to start with, then add 2nd. Use one of the PCIe slots for your SSD(s). Maybe start with a 500GB.
Maybe use JBOD to combine two but not in RAID0.
The system can go on SATA II drive bay or optical bay.
Is there a one size fits all or to say this is the only way? of course not, you can though test and try and work with your budget, your Mac and move SSD to where it does the most good.
Samsung starts mass producing PCIe SSDs with 1400MB/s read speeds
When the new MacBook Air got the teardown treatment... a new SSD.
The new drive is known as the XP941 and Samsung will offer it in 128GB, 256GB, and 512GB configurations. It achieves read speeds of 1,400MB/s, which clocks it at 2.5x faster than a SATA SSD. It also only weighs 6 grams and measures 80 x 22mm. Samsung claims it only takes up a 7th of the space occupied by a typical 2.5-inch SSD.
SSD Maintenance
https://discussions.apple.com/thread/5012276
Samsung 840 Pro and Samsung 840 Solid State Drives Reviewhttp://www.xbitlabs.com/articles/storage/display/samsung-840-pro.html [06/07/13 | Storage ]
Samsung currently offers very interesting solid state drives. Some boast outstanding performance, others – are built with inexpensive TLC NAND and come with a very appealing price tag. And our tests prove all of this: we are ready to discuss what we saw when we got our hands on a Samsung 840 Pro 256 GB and Samsung 840 250 GB drives.
From last September, StorageReview article 840 vs 840 Pro - they were my favorite review site for storage for years.
http://www.storagereview.com/samsung_ssd_840_pro_review
Second only to TechReport
http://techreport.com/review/23990/samsung-840-pro-series-ssd-reviewed
X-bitlabs is also one of my popular stops and they look at Sandisk
http://www.xbitlabs.com/articles/storage/display/sandisk-ultra-plus.html
I am sold on Samsung though and feel the 840 will do fine for me, but I would use $$ to get Sonnet Tempo SSD or Pro from OWC.