I currently use one of these plus 3.5" to 5.25" brackets to mount two 2.5" drives in the lower ODD bay.
But because I'd like to add more 2.5" drives, this thing is going to replace the current carrier.
Power and SATA connectors are no big deal, since you can get adapters for almost every connection.
Just make sure how many drives you'd like to put in there, that makes recommendations much easier.
If you want to drive a RAID0 out of two SSDs, you definitely need a dedicated RAID card, otherwise the ICH10s maximum bandwidth of 660MB/s will throttle the SSD array.
Considering that you currently got 4 drives in your Pro which have an approximate bandwidth of 400MB/s, a single SSD would be possible without a RAID card.
nanofrog always recommends the
ARC-1210 (or 1212) for the Mac Pro and such requirements. This is the way I'm going to get as soon as my 160GB are full.