I want to install the OWC Mercury Extreme Pro 6G SSD as the main drive and a cheaper 3G internal 1tb hdd for media in the optical bay. Will these drives both perform at their max speeds or will they both perform at the lowest speed (3G)?
They will both perform at max speeds. The first mbp's only had SATA 2 for the ODD anyways, but it really doesn't matter since a 1tb hdd won't saturate a SATA 3 connection anyways.