NV30 peformed pretty well against R300 in then-current games; it was next-gen, SM2 benchmarks that exposed its weaknesses. I don't believe R520 will be weaker than G70 in SM3 games or benchmarks to the same degree NV30 was weaker than R300 (1:2), so really all we have is a pretty significant (because G70 is already here) delay, but still not NV30 length (which was six months, IIRC).