lens - Seriously considering upgrading my Rebel T2i (550D) to either a 6D, 7D or 70D

I shoot a lot of performers in low lighting conditions. Essentially I am looking for a camera that will help me reduce the noise level significantly. I find myself rarely using the kit lenses and mostly using my canon f/1.4 50mm prime which is fantastic in low light and night time but, I do have limitations in spaces where I am too close to the subject(s). This is where my debate comes in about about purchasing a 24-70mm f/2.8L series lens or purchasing the 6D, 7D or 70D plus the 24-70mm f/2.8L lens.