<< What I want to know, is what will be the extra features when going from the MX460 to the Ti-4400? >>
Well with the former you're getting a crippled GF3, and with the latter you are actually getting a GF4. They are not based on the same core at all. The GF4 will kick the crap out of the GF4MX no matter how much you overclock it. The GF4 has 4 pipes, the MX has 2. The GF4 has the next gen nfiniteFX engine, the MX doesn't even have all of what makes up the original nfinitefx engine. The MX460 might be able to overcome the GF3 Ti200 but that's about as far as the MX's are gonna get performance wise.