The HD2900XT is not designed to compete with the 8800GTX. It's direct competition price and performance wise is supposed to be the 8800GTS. The fact that it can compete to some extent with the 8800GTX is just icing on the cake.
The HD2900XTX will be released later (Q3 hopefully), featuring 1GB of GDDR4 ram. The suspicion at [H] is that getting proper yields of GDDR4 memory available to run for the HD2900XTX is holding things up. Which sucks because look at what the 8800GTX is doing with 1ns GDDR3 right now. The HD2900XTX will be basically using twice the GDDR4 ram as the X1950XTX currently does (512MBx256-bit scaled to 1024MBx512-bit, so double the 32-bit IC's for the memory bandwidth).
Sure, you can RUN Crysis, but will you want to? At 1280x1024 my 5900XT crawls when you get 15-20 EMP patroit's firing on C&C: Generals. And that game is several years old. The 128MB 5900XT is WAY over the system minimum requirements, but there is a difference between playing it stripped down and lagging on a 6600 vanilla, or playing it with things cranked, 1600x1200 on an 8800GTS. Get what I'm saying. I can play today's games on my 5900XT, but I don't - it's not worth it to ruin a good game by forcing it upon crappy hardware.