Narlus is right, not that much difference in price, especially in the coming months as Canon will probably have to lower prices to compete with the new Nikon offerings. Plus, any cheap 5Dc is probably very well used, emphasis on "very well" 
I shot for years with 5Dc, and even with f/2.8 glass it is still hard to get decent concert shots. So save your money and imo, rent 5d MkII once and try it out at a concert before buying.
Also, make sure your glass is top notch, no sense upgrading the camera if your lenses aren't up to the task. If you aren't using primes or 70-200 II 2.8 or the like then you may want to consider investing in better glass first before a new camera. Glass lasts for years, new camera technology always changing.