I'm not 100% sure but if the markings go like with AGP cards, the 420 is a dog with SDRAM. It's as slow as Gf2 MX400.
The 440 should be quite a bit faster, but not blazing fast.
If you asked me, I'd tell you not to buy a MX card, invest to Gf2 ultra or Gf3 ti 500 even.
Edited for brainlapse: For PCI you're stuck with those.. D'oh!