I haven't found many charts yet on google, but i saw one on this website that cited the average READ throughput for WD 10000 rpm raptor as ~160 MB/s read
speeds, which is well under SATA 2 max MB/s throughput
, which allows up to 300 MB/s
Even the MAX read throughput on the raptor (which is basically the fastest there is) was only around 200 MB/s.
As I see it you might as well leave any other SATA 3 ports open for SSD only use.
EDIT: Here is the link to the benchmarks on this website, so you don't have to take my word for it: HDD Benchmarks