When I had PI cams, the ideal shift point was still way up there (6500+). So the limits of your shift point will likely just be your valvetrain limits and where you feel comfortable running it to. I suspect it'd be fine to up close to 6500 on all stock stuff.
With stock size tires (25.66") and 3.73s, 120 mph would be 5863 rpm. 125 mph would be 6107 rpm. 130 mph would be 6352 rpm. So as long as you are ok with turning 6300-6400 rpm, and don't plan to go over 130 mph, the 3.73s are certainly ideal for the track. 3.90s might actually be more close to perfect if you're only going 120ish, but I personally wouldn't run a non-Ford gear, and you wouldn't have as much room to grow at that point (6500 rpm would only be 127 mph). And even if you did move up into the 130 range, it's probably be good to start looking into a taller tire anyway.