Eh, I'm still in warranty, so what the hell. I'm posting from my 5,1 Pro after updating to 1.8. I have the 7.99 ebay generic optibay knockoff, with a 128 GB Kingston SSD in it. Scorpio Blue 500GB in regular HDD bay. No problems updating, Pro started right up. System profiler shows the chipset is still operating a 3 gigabits, so nothing funny happened like knocking the optical drive down to 1.5.
I haven't applied the actual superdrive update since my superdrive is 30 miles away at the moment. Probably won't ever do it since it probably won't ever get back into my Pro.
Ran a few apps that hit the Scorpio for storage, no issues. Fusion starts my Win7 VM, iTunes still sees my music, iPhoto sees my pics. I'll know better after a full day's workload, but for now I'm calling it a success.