I'll see if I can talk wifey and 3 kids into a stop soon.

Back on topic... I think the 2.5" stock exhaust is nearly maxed out with the K04's. If you look at the 2.7t guys with 770's, quite a few have 3" exhaust, if not all. The interesting thing is I saw one 770 2.7t build with stock exhaust manifolds. I think this my be purposeful and help spool faster. Backpressure is important but it must be balanced with air volume. If 770's mate up to stock 2.7t exhaust manifolds then your stock RS6 manifolds should work as well. Go for larger downpipes if budget allows. Otherwise, keep 2.5" stock dowpipes and gut precats. That is common man's method of upgrade. Keep us posted on build. that will be a monster. I assume you are rebuilding internals also? I'm sure if you did a 2.7t with 700's you know the drill.