Hi Riskas,
Like Tim, I also have both lenses on a 1DsII & 1DII. Since you are using a 1.6x crop factor camera, the 24-70 will probably work fine for portraits, people, etc. And if low light performance is a priority, the extra stop is going to be useful.
I would probably go the 24-70 route based on what you've posted. You might want to look for a good, clean used sample, as some folks have "retired" their 24-70 for the 24-105, although I'm keeping both for sure. "IF" you were using a 5D, I'd say go with the 24-105 as the noise at ISO 800 is remarkably low compared to even my 1II series cameras & I suspect the 24-105 would be useable even for low light stage shots, etc (at ISO 800).
I have to admit, since getting the 24-105, my 24-70 hasn't seen much use for the kind of work I do. I really like the 24-105 ALOT. It is very sharp and the IS is a nice feature. Plus the smaller size, lighter weight, extra reach, is a real plus for my six decades old arm .
Tony