I got my SATA splitter (had to, thanks to Apple having an all-in-one power/sata cable).
Now have my Samsung 840 Pro 256GB SSD booting Mac OS X and Windows 7 (both 64-bit) via cheap-ass ASM1061 SATA3 card (also have two eSATA ports as well)
I haven't been able to do a reliable benchmark, but Win7 Experience Index jumped from 7.7 to 7.9, so there was a major improvement. Benchmarks with screenshots to come soon. For now, check out the relatively neat job I did...
Win7 only showing 390/360MB/s read/write speeds :-/
When I had my Core-i5 Win/Hackintosh, with motherboard SATA3, I am sure I was getting better speeds than this (540/490) but the card has overheads, and I am just glad I am now getting more than x1 speeds of 250/250 
Mac OS X and Windows 7 now both boot about twice as fast, which is helpful as my non-EFI firmware graphics card does not show any boot screens until the Desktop (including Alt-key bootloader).
PS. While I was in the Mac Pro, I discovered I had thrown away the rubber (silicon?) gromits on the optical drive screws. I fashioned some out of blu-tac, and reinstalled the Blu-Ray burner, now the machine does not vibrate itself to death every time I use an optical disk (although it is *very loud* still).
