ah, the eternal PC builder's question... upgrade now? or wait? Only you can answer the question, but here are some things to consider:
1) Will what you have now work for the next 3 months before the new cards come out?
2) Will the currently available upgrade work for what you need it to do?
3) Will the currently available upgrade work for what you need to do in 2 years?
4) Will SLi or xFire be a viable option in 2 years when you need an additional cheap upgrade?
5) Will the new card provide a significant performance gain, lower power requirement, Lower cost, or additional features? (in this case; yes, yes, maybe, and no)
6) In the case of GPUs, will a sufficently fast GPU be released with the release of the new series? (generally low/mid range GPUs are released first, at a premium, to be followed by higher end cards, and cheaper low/mid range cards).
In general I would wait unless you particularly need it now as they will be out in a mere 3 months.