Kyle from [H] says it is 680,
Seeing some benchmarks show 7970 in the lead, mostly in tessellated situations there, other "normal" synthetic 3D benchmarks and gaming benchmarks show 680 faster. Driver advancements still happening as well for 680.
If it's actually $400 (with a die size below Tahiti and only 256-bit memory bus that seems quite possible) this will surely shake things up! That would mean 7970 coming down $150 and everything else following by around $100-50 or so.