I've owned and used a 5D & a D90, the D90 was sold on fairly quickly, but I've had a love hate relationship with the 5D - I've owned two at different times!
The D90 is good for tracking moving targets and gives bright cheerful colours - good for general holiday use. What spoilt it for me were the better landscape colours from the 5D and L glass and the infuriating habit of randomly blowing highlights, the D7000 does this as well. The D300 & D5000 are much better - best Nikon for not blowing highlights was the D200.
The 5D has much better noise at 1600 iso on screen, but this doesn't translate to better on an A3 print. Focus with the 5D is slow but great if you use L glass, especially the L f2.8 optics - a 70/200 L f2.8 II should be a killer for gigs! Focus much poorer with slow non-L glass. Landscapes are superb with the 5D on a screen, A3 prints have more detail in grass and complex areas - 3D effect from higher micro-contrast L glass. What is annoying is the weight, expense and the fact that the 5D is ruthless on edges - you'll find that not all L lenses are made the same - you have to cherry pick your 17-40 to get one that is edge to edge sharp for landscapes! The 10-22mm Canon has better edges than the 17-40 - you can loose all the advantage of FF if you end up cropping!
Nikon APS lenses are generally better edge to edge, I just prefer lanscape colours from the 5D. For portraits the D200 is best in my experience.
I've taken the 5D on hols with all L glass, but it's very heavy and attracts unwanted attention! I've used a D5000 with great results hor hols focus just as good as the D90, viewfinder is crap.
I'm moving over to Panny G series now.
Hope that helps.