Dave,
There's been some guidelines posted by guys who know engine work. I agree the clearances and running temperature seem to be the key factors in picking the weight (SAE grade for those who like to be technical). Let me see if I can find the posts, I think they were at Moparts or Speedtalk.
here's one - Oil Viscosity vs Bearing Clearance
But its hard to go wrong with a 10W-30 in an engine that's not worn or purposely built loose.
I've been using Brad Penn in my 340 but the lift is only .503 or so. It seems to be a quality base stock and a good zddp antiwear package. Since the engine runs a little on the cold side, and at autocrosses there's little opportunity to get the engine up to temp, npomrally use 5W-30 or 0W-30. The one time I took it to NJMP I brought some 10W-40 in case the oil temps started running much hotter than normal.