From what I recall your cam was 265/270 @ 050 with not much lift. Something in the mid 0.500 range? So that could be just a tad small for the cubic inches and RPM. Since the car is running really good I might stay with the same lobe family and just go up one or two sizes on the cam. But other people have good suggestions on checking for adequate fuel pressure at the top end. You hate to spend a bunch of time and money changing the cam then find out you have clogged fuel filter or something like that. I'd think that cam would pull to 7000 but perhaps it is just running out of air. That is where the dyno sheets would've been a big help.