Advice on Cylinder Head cfm for 340 stroker

The Victors are at a whole other price level, I was at the local machine shop yesterday when I found out the trick flow heads would be delayed again.... the owner of the shop said let’s price some Victors out... he stop himself when it passed the $5000 Canadian mark ... looked at me and said you would have to be nuts to even think about them...
Yeah really. Victors, w2's, all high priced options on their own not to mention scrapping all my existing valve train, intake manifold, tti headers, etc. Not worth the cost and hassle when similar flow numbers are available from less expensive, standard valve train, standard intake, exhaust port heads. This all makes the Promaxx look like the best bet as long as I'm not restricting the engines potential by a huge amount. I'm just in the dark about what the noticable difference on my build would be between 285 and 300 cfm/intake... are those last 15 cfm only usable approaching my 7k rev limit or do they affect the entire rev range?