Vizard has stated pretty specifically that flow during OL is far more important than suspected previously.

When heads are flowed, is that with a 12.0:1 CR domed piston below the (partially open) valves?
At full lift, there is almost no intake vacuum, while (assuming a good exhaust) at OL vacuum from the return pulse may be 7".

Flow bench: useful
Dyno: more useful
LSR: most useful