Why do the high end and value cards all have to be named the same!?! I am sure that Nvidia has throughly confused the average consumer. I think the Ti4400 is faster because the FX is a value card. IF this is being used for mame, currently there is no reason for a better card then the one you have.
Also, if you are using a tv, ATI's tv out is vastly superior to nvidia's. I was amazed by the difference in quality when I compared the radeon 7500 (in my arcade) to the GF3ti500 (in my desktop).
I really doubt you have any reason to make that small of an upgrade.