based on your current performance,( heads you have already) i would expect a set of well done eddie heads to be 2.5- to 3 tenths better than what you have currently. Not to mention a pretty decent weight savings, that you can factor in as well.
knowing what i know now, and people i have talked to over the past few years, i would recommend the hughes head and the full cnc porting they offer. you are just going to have more uniformity cylinder to cylinder over hand porting, and hughes's cnc program is on the agressive side as well, they produce a nice head, a local friend just ordered a set for his 408 ...i dont see any reason whatsoever you shouldnt pick up at LEAST 40 horsepower over what you currently have, if not a little more.

there are other heads that obviously will offer a bigger gain( indy/w5, etc) but if your goals are as you stated above, the cnc eddie heads from Hughes are, IMO, easily capable of the upgrade in performance to suit your requirements.
they do a lot of work with iron heads as well, give them a call and ask their opinion of a max set of eddies compared to your j heads.