I went with the 6D over 5D2 when I upgraded from mk1 5D, as it didn't feel like I was getting very many upgrades for my £, whereas the 6D seemed a whole jump on, ok still only 11 focus points but still better than the old 9. Looking at 50D vs 5D2 looks much the same, you gain full frame but that's about it. SD vs compact flashes nags at my "well it isn't as good" but I do like the fact they're small, readily available in every town, and hasn't actually affected me in any way really, and neither has the 1/4000 shutter limit, except when a customer loaned me a 85mm F1.2 for an afternoon, and I wanted to shoot at F1.2 as you do.
Wifi & GPS as built in features just add to the bargain of the camera to me, as man maths mean you can argue you get the camera for free, and the performance of the liveview, which was a feature I wasn't bothered about when I ordered it, but first week with it, on holiday, on a beach, 10 stop ND filter on, press liveview "wow", quick increase of workflow, and it's readily accessible rather than being hidden away as an afterthought.