I believe you mean SATA 1.5Gb/s and SATA 3.0Gb/s?
Is the Seagate ST3 1T as 1" HDD? I can't find info on a "Seagate ST3 1T" or "Seagate ST31T". If so, it basically does not matter since it will never even come close to hitting 100MB/s.
Generally, the SATA generation mode does not improve performance unless the drive is capable of utilizing the addition bandwidth.
I think this post needs to get moved to the motherboard support forum and not the SSD forum, no?
I agree the post should really be under motherboards.... or actually with Seagate. However, if the issue could just be resolved now, might as well try.