No problem at all.
I have a Samsung 830 64gb in my HTPC which has a Gigabyte GA-MA78GM-S2H (rev1.1) which has 780G northbridge and SB700 southbridge.
Of course the read/write in CrystalDiskMark etcetera synthetic benchmarks are lower with SATAII but it's still fast, more than enough speed for having it as a boot drive.
Compared to a newer southbridge (w/ SATAIII) you'd have faster read/writes but that's about it.
tl;dr, just go for it
BUT, I would be vary about that Phenom II X3.
Is this your motherboard?
http://www.jwele.com/motherboard_detail.php?419
I looked at the VRM area and doesn't look that strong so if your Phenom is a 700e or 705e then okay but if it's one of those other, with 95w TDP I would STRONGLY recommend adding some more cooling to the board, like the Enzotech MOS-C1 would probably fit fine here.
Even if your Phenom is one of those 65w TDP models then I wouldn't even try overclocking. If that motherboard has voltage adjustment ability in BIOS then I would strongly suggest lowering the vcore as well. Don't know for sure but it looks like 4+1 VRM at best.