I have an 80GB Velociraptor as an OS drive right now. I saw that I could sell my velociraptor for ~$60-80 on ebay. I could buy a 60GB OCZ Agility SSD on Newegg for $170 AR. Would I see a noticeable improvement in load times for Windows and GTA IV? Would an SSD change the game experience at all?
You'll definitely see faster load times, but once everything is loaded up the game probably won't run any faster. The exception would be if the game needs to access the disk, perhaps at a scene change or if you don't have enough RAM to fit everything into memory.
RAID 0 doesn't improve access time significantly, so two SSDs in RAID 0 (or any other RAID for that matter) aren't going do boots and loads much faster than one. If you're going for that kind of performance then go for the SSD that benchmarks best for random read I/Os.
I know RAID 0 won't help the access times at all, but a higher transfer rate can't hurt. One review showed the Patriot drives getting 205MB/s and in RAID 0 380MB/s. That's a lot of transfer over the Agility.
The first link below shows results of both SSD's. Do 4K transfers relate to access time somehow? The third link shows that the Agility has access times of 0.242-0.315ms. I couldn't find the Patriot's access time, but Newegg reviewers reported 0.9
I've also just found the OCZ Solid 2 Series 60GB for $169 AR, but I can't find any reviews of it.