If noise is a concern to you then the 5D is much better than the 50D (when I tested them it was about 1 to 1.5 stops once you get over ISO 400). Your problem will be that your wide angle will not work on full frame (though the 24-105 is perfect on a 5), so you will either need to swap that for a full frame lens, or not have a wide angle for the 5.
Actually for the stuff you shoot, it might be nice to get a 5D and then sell one of your bodies for a 1D2 (considering that they are down to about £500 used now). Both of these cameras will have better high ISO performance than your current cameras.