dude, get a grip. he's going to be running 1920x1080, not 2560x1600.
4.8 GHz DDR5 is more than enough at 128-bit. my concern for him is the larger amount of compute power, new shader model, programming APIs and energy efficiency.
RV740 has been a great demonstration that a small (15-20GB/sec) discrepancy in memory bandwidth (compared to 4850) is not going to catastrophically break your high-res/AA performance, and the total number and clock freq of shaders is still the biggest determination of performance. The Radeon 4890 demonstrated this also because its high performance fab process allowed the core to achieve significantly higher clocks, meanwhile the difference in memory performance was smaller than even that between 4770 and 4850: The 4890 has a mere 9GB/sec faster memory than the 4870; the bulk of performance improvement with RV790 is not at all attributed to a mere 300 MHz bump in memory: it's in the core.
I understand your concern at very high res, but 1080p isn't very high res and as long as there's 80-90 GB/sec on 5770, he's going to be in great shape. the size and speed of the GPU are the primary concerns. i'm not saying he should commit to the 5770 before it comes out, but buying a premium-priced obsolete card is even more foolish. everyone considering a new GPU, at this time, should absolutely wait for reviews regardless of what the market looks like now because, fast or slow, the introduction of 5770 will result in a cascade of price reductions in all segments. in the very unlikely event that i'm horrendously wrong and 5770 ends up being a complete reversal of previously demonstrated architectural trends, then whatever, i was wrong, big deal. by the time that happens the 5850 will be around $250 and that's the card i'll be cramming down his throat instead.
but since i've come this far and said this much, i may as well lay out my prediction:
below 1900x1200, the 4890 is going to be surpassed by the 5770. at high res, turn up the filters a little bit and that behavior is going to begin to reverse, but I don't think a 4890 is going to put a 5770 to shame by any means.
you're talking about ~30% more GPU power and ~30% less memory bandwidth than 4890. it's going to be too close to call, so the more efficient, feature-packed card with higher net FLOPS wins.
