I'd look on ebuyer for the best deal, should be free delivery around that price range
I'm pretty sure SATA 3.0gb/s is backwards compatible so it should be fine, anyone else care to verify? :)
as for 7200rpm vs 5400rpm in a laptop drive, I'm not up to date on that, I've never used a mac for more than 10 minutes but I'd get the 7200rpm one, the seagate ones will probably bit quieter