I realize this is an old thread, but...
The stock 300 six/4.9 efi cam has quite a bit of advertised duration (~268) but the ramps are very mild. I assume this is for longevity more than anything else.
When building my 4.9, I was initially going to use a Comp 260H. When I discovered (on this forum) that the stock cams have 268 degrees of advertised duration, I went for the 268H instead.
Observations:
The Comp 268H has a .050" duration of 219 degrees. That's a fairly aggressive lobe. Being a flat tappet cam, it has a faster off the seat rate than a roller lifter will allow. You can tell how aggressive a lobe is by the number of degrees between the advertised and .050" numbers. Tighter means more aggressive.
The lobe center of 110 degrees causes this cam to lope a bit at idle (overlap 48 degrees). But the tighter lobe center lowers the rpm at which peak torque and HP occur, too. These heads do not require split-pattern cams (both carb and EFI). The exhaust ports flow plenty of air compared to the intake side (and compared to 5.0L exhaust ports, which do favor a split-pattern cam with more exhaust duration and lift).
A stock 4.9l really runs out of breath by 4000 rpm. My Offy DP- equipped (390 Holley) EFI-manifolded 4.9L will float valves easily at 5000+ rpm if I'm not careful. I attribute this entirely to the cam. The head is a mildly reworked EFI head with stock valves. Total ignition timing is set about 35 degrees.
I'm in the process of re-doing the exhaust right now. Hedman hedder, full 2" duals with a crossover (staggered to the length of the dual header outlets, ugh!), Super turbo mufflers. According to Dyno sims this will actually lower peak torque to 2000 rpm or less...