Upgrading 7280 to version 4 should be no problem. There are rumours on the net (other BB forums) that the 7290 will not be running version 4 when it is released, it will be running version 3.8 like the new 7100T/7100V. If you do not need bluetooth and the more of RAM, than you should get the 7280. Else wait for the 7290. For daily usage I think the different displays shouldn't matter, that's mho.
I have a 7230 and a 7730 and I am able to compare both displays.