Well you could go with the GF4 and an FX5200, just don't expect much from it.
Even a GF4ti + another GF4ti may be a better bet. But the FX5200 should give you slightly better 2D quality.
If you have to buy another card, then maybe enjoy the slight upgrade of an R9600 (not pro/ not SE) for just about the same price (seen it for $75). But you're kind of between a rock in a hard place, and no one here wants to recommend an FX5200 for just about anything. The GF4ti is a better card IMO, and the R9600 is the match of the GF4ti with one doing better than the other in different benchies.
Not an easy call nor an enviable position.
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