This close to march, I'd say stick with your 4890. That card is already capable of maxing every game and there's no real need for 5870 unless you're going eyefinity.
Also I'd go with the meghalems, if worse comes to worse, looks like you could rotate the heatsink since it's rectangular. Then just ghetto strap the fans on with tie wraps or something. I'm just eyeballing it though so don't quote me