I'm not a head porter so I don't know. I do know from having seen guys here porting and testing what changes yield increases in flow, a 20cfm jump seems like a pretty big deal, especially if you're already starting out with a refined head like the TF
From what I've notice that most street strip type builds fall in the 1.7-1.9 hp per cfm range, some get 2+ hp:cfm, so I use 1.8 as average reasonable power potential.