You raise a good point with the Video Memory consuming physical RAM. Users with integrated graphics are better of setting the shared RAM to the minimum. A GeForce 6100 could never make effective use of 256 MB of texture memory; 32~64 would probably be optimum.

It's not generally true that external graphics chips have better 2D. This was true maybe 3-4 hardware generations ago, when integrated graphics didn't even hardware accelerate vector surfaces or mouse pointers. A GeForce 6100 is feature-superior to a GeForce FX 5200 in nearly every way.

Most GeForce FX 5200 would be slower than an integrated GeForce 6100 (with the exception of the GeForce FX 5200 Ultra) in both core and memory bandwidth.