There are pros and cons to both...I have run both, and had great results either way. I run the closed chambers now on my 505, because I already had them. I pretty much did what you said above...milled, mild porting, etc. I was able to get a 10/1 c/r with flat top pistons. Like you said, the flame travel is better without the dome in the way. But I dont think it's a huge factor either. I like the closed chamber heads. I know a lot of guys who are running them in a drag car and do very very well. John