I'd go with the 4 type r's...i didnt like the way that the type x's sounded anyways. Listen up...if you get the dual 4 ohm subs then you will need an amp that puts out 2000 watts rms at 2 ohms or .5 ohms. But if you get the dual 2 ohm subs then you will need an amp that puts out 2000 rms at 1 ohm. I think you should stick to the dual 2 subs IMO..
Also, make sure your car's electrical can handle the amp. I'd recommend the Big 3 upgrade, an extra battery, and a high output alternator (if possible). but running a 2k rms amp on a stock electrical will create some problems, and your amp will probably blow.
As for size, 12s will be louder. Given the right enclosure and power, 12s can sound just as good as 10s, so get the 12s and start making some noise.
Cheers...