268/272/372XP's are excellent saws, and very close in power. I've used stock 372XP's with 24" bars and they are fine, but pretty much maxxed out if you want to run that much bar with great authority. All of those saws will run a 20" bar at any load in any material. They would be OK with a 28" bar, if the operator didn't push them too hard. The 372XP's like rpm's and stall against the clutch quickly if you really dig in with the bar buried. In big wood it really comes down to the operator more than the saw. If you are keeping your chains razor sharp, and saw finely tuned, the 28" bar would be fine, IMHO.
If you want a saw that runs a 28" bar with great authority in hardwood, move up to at least 80cc, 95 to 100 would be even better.......Cliff