256GB SSD with two partitions?

There are different levels of performance from each card in each generation. The 2nd and 3rd number indicatre the relative performance in that generation (1st number is the generation of the card). So a gtx660 = the 600 generation cards, and is a 6/9 on performance scale for that generation.

Gtx750 = the 700 generation cards, and a 5/9 on performance scale for that generation. Each generation they make improvements to performance and power usage over the last. But the amount of performance varies.

The gtx750Ti is pretty close to the performance of the gtx660. But the 750 is quite a bit lower. Even though its only 1 number away, the performance difference is a pretty big step.

Its usually like that with all "mid range cards" vs "high end cards". There is always a gap between them. The gtx660 is the start of high end cards, where as 750 is a mid range card.