Well it depends...
Overall speed is better with SSD (the system is more responsive etc). Gaming speed will depends (mostly) on GPU (in rare cases the CPU can limit it... But only limit) and heavy calculation and so on CPU...
get i3 series or low-end sandy bridge i5 2300 and get a 128gb ssd.
Personally, i'd go for i5 and then use the spare cash to upgrade the video card.
SSD will only affect your boot/games loading time, but will not improve your frame rate or graphic quality.
Unless you put that Pentium G620 on a z68/z77 motherboard, you will need to upgrade the motherboard to overclock the 3570k.
If you can't OC (due to low/mid-range chipset) and do not plan to upgrade the motherboard, you might want to shave $20-50 by going with the i5-3470/3550/3570.
i beleive that the 650 gtx is faster than the 7750, and so id say i5 and new z77 motherboard, i7s HT is not used in most to no games. A new cpu plus motherboard is more expensive than a ssd, so could go for the ssd later, i mean if u just get the cpu or ssd, why spend more in a ssd than ur $80 cpu lol