A few salient points here:
The newer DSLR sensors are champions at high-ISO performance. Nikon's D700 and D3 series yields very impressive performance at ISO 1600. Older DSLR's could not match this performance in my experience.
Film is expensive. 400X more so, and medium format more so. Film is expensive to process, and pushing film tends to require a good understanding of what happens to the curves and colors, not to mention a consistent lab to accomplish this (which are becoming sadly more and more scarce these days. Film is expensive to print or get good scans made from. With film you are dealing with a latent image that you will not know what you have until it's too late to shoot it again (given the OP's desire to shoot at concerts). That said, if you were choosing film to shoot fast color, 400X would be a very good choice.
Medium format is definitely not the best camera format to shoot concerts or fast moving action with. Lenses focus slower (either in manual or auto-focus) and the cameras are larger, heavier, and much more expensive (though great deals can be had on film cameras). The medium format digital options are extremely expensive and are not great at dealing with fast moving subjects. I've been using a Phase P65+ for a project recently and tried using it for some hand-held fast-moving subjects. Bad choice. Very slow. I could get far better results in terms of capturing critical moments with my D700. Of course it will not have the image quality of the Phase, but not many people need that unless you are constantly blowing up to poster-size.
Shooting with a 1.0 lens is a valid suggestion if you happen to have the $ to buy one. Why not go for the Leica Noctilux f 0.95 at around $10K from B&H? What will this accomplish? At 1.0 you have virtually no depth of field at all. If your focusing is not spot-on you have a series of soft images with lovely bokeh. Using a DSLR the faster lens allows you to see a clearer image in lower light through your DSLR finder, for whatever that gets you. You still need to be able to focus it dead-on to take advantage of its widest opening (which, by the way, does not yield optimum sharpness or consistency across the image from corner to corner). You can produce some very beautiful effects with it. Certainly it is an advantage for shooting in low-light, but a very expensive one at that level. A 1.4 lens would be a fine choice too and some of those are quite good at their widest opening...still, no depth of field at all at the widest openings.
If you are seriously into shooting concert images, a much better investment than a 1.0 lens (and a bit more affordable) would be a good VR lens, like Nikon's excellent 70-200 2.8 VR zoom. The vibration reduction feature is very effective and will get you great results for use in low light (you can hand hold at around 2-stops slower than you would otherwise normally be able to). BTW, the only 1.0 lenses I know of are 50mm. For concert photography, unless you are standing on the stage, your images would be rather limited with such a lens shooting from the audience.
Good luck!
