Sounds like you have a 3,1 from 2008. Although you can't do a lot better in the CPU department, you can add everything treestar talks about but Thunderbolt, and who needs TB anyway? You have PCIe, and can add USB3 and SATA3 cards plus a better GPU (with HDMI) if you need it.
How about an SSD for your boot drive? If you haven't gone there yet, just do it. You will be very happy. Don't worry about SATA2 or 3. Just do it. And while you are at it, note the space in your current MP for expansion... a thing in the nMP's past.
If you want a new toy, the nMP will assure you of a painful and spendy upgrade that will constantly remind you how "new" it is.
Used/Refurb 4,1 and 5,1 MPs will abound in the months ahead, and you can do a hell of a lot with a lot less money with one of these. Look into a 4,1 single-CPU for <$700, flash to 5,1 for free and upgrade the CPU to a hex 3680. You'll top the top iMac and almost double the performance of your current machine. Or, if you are using heavily multi-threaded apps, get a used or refurb dual processor 5,1 and live large with 12 cores. You can upgrade CPU and GPU there, too.
You'll probably only notice the difference between SATA2 and SATA3 when backing up drives, and then only if you are backing up SSD to SSD. Sooo... drop in a SATA3 card if it's an issue. Same with USB3.
The nMP is an incremental performance upgrade in a *neat* case which abandons inexpensive and readily-available expansion in favor of costly Thunderbolt, largely to the customer's detriment.
Dem's my thoughts.