Never Raid Before Need Some Advice

You need more storage? The most immediate flaw that I can see in this plan is... initializing RAID-0 wipes both drives.

Drive technology has come a long way since the 640GB drives. I'd probably skip the whole RAID thing and just buy a new 2TB drive. It's going to be faster than your 640GB, so you can move your games and stuff over to it (keep OS on the WD Black) and then store stuff wherever you want. (maybe partition the 2TB in two; games on the first partition, storage on the second) The best part about a setup like that is, OS/Apps can't interfere with your games. No stutters if AV decides to update itself, or something else gets busy in the background.

RAID-0 nearly doubles sequential speeds, but it does nothing to improve access times, so often the boost is more like 20-30%. A new drive with denser platters will probably be 20-30% faster as well. So basically, a single 2TB 7200RPM drive will likely match a 2x640GB RAID-0 array. (except in perfectly sequential file copies)

RAIDing different SATA types and cache sizes is fine. The main requirement for RAID is both drives have similar performance levels. You can benchmark both drives with HDTune to verify they're within a few MB/sec of each other, and have the same access times.



The array performs as slowly as the slowest drive for each characteristic, so if you RAIDed a WD Black 1TB (120MB/sec, 12ms) with a Hitachi 7K1000.D 1TB (160MB/sec, 17ms), you get an array that performs under 2x120MB/sec with 17ms access times.

With different brands NCQ algorithms may also not match up, causing the array to underperform when queue depths go up. (Basically any time the drives must multitask)

Mostly just googling. Many reviews include HDTune benchmarks, and boards like these often have HDTune results for various models - there's even a thread with plenty of results, but many are for RAID arrays.

I think the 1TB models use 500GB platters, while the 640GB Black uses ~333GB platters? 1TB Blue/Black would likely be 20-30% faster. I'm not sure where a Green would score... probably faster sequential speeds, slower access times. Factoring both in, it would probably be slower than your 640GB Black.
50-60GB is probably enough, as long as you're sticking games elsewhere. Many people with SSDs get by with that little.

Keep in mind if you want Hibernation enabled, that uses up as much space as you have RAM.

You could go with less if you have a vague idea of how much you'll need. I think I'm using about 18GB with Hibernation and Pagefile disabled, so probably 30-40GB is the bare minimum.