What you do in this case is get the kit with the 24-105L lens. This solves all of your problems.
That's what I said :-) ... @squarebox: Maybe have a look at your Lightroom stats again, how many shots did you do with open aperture - so is f2.8 really necessary considering you've already got the primes? And then look at the LR stats for zoom length (you can create a smart filter for this, zoom lenght > x and < y) - is dropping the 70-105 range on the zoom a good idea :-p ?
That's a great way to look at it.
Looking at my stats from the 24-100mm range, 80%+ of my shots were at max aperture, which might not help cause we are talking in the range of f3.5-5.6.
The other thing is that moving up to FF should get me a few stops increase in light performance, so when i see apertures i'm thinking how they work for me on the crop sensor and with weaker ISO capabilities. So just by moving to the 5D, F4 might work for me.