I currently have a SATA2 Intel 320 Series 120GB SSD (connected to my ASRock P67 Extreme 4 Gen 3). My motherboard has SATA3 ports, and with the recent price drops on the SATA3 Crucial M4 SSDs I'm wondering if it would be worth getting a 128GB SATA3 M4 and moving Windows and some programs (Adobe Suite, Office) to it and using the 120GB Intel exclusively for games.
Would I notice a speed difference, significant or otherwise, between a SATA2 SSD and a SATA3 SSD?
You probably would not notice any real world performance difference between modern SATA 2 and SATA 3 ssd's. You would have to use a synthetic benchmark to be able to measure the small performance difference. It would be different if you were doing some sort of high end scientific or professional work. It does not sound as if you are.
There's more to an ssd than just how fast Windows loads. What about real world performance using real world applications? Doesn't that matter too? That puts the entire situation in a new light. With modern ssd's the general rule of thumb is go for a larger capacity instead of synthetic benchmark performance. Those benchmarks are called synthetic for a reason. They are not real. They do not accurately portray real world performance. At best they are a way to grossly exaggerate minor differences. Companies pick and choose different synthetic benchmarks to make their ssd's look good.
Here are three articles Tom's Hardware published that you might want to look at.
SSD Performance In The Office: Nine Applications Benchmarked: