GeoKras,
I love the 15-85. I've used it on my 60D and now on my 70D (though I still have the 60D as a backup). My wife loves hers on her SL1, even though it's much heavier than the camera itself. We both use the 15mm end of the lens quite a bit and that's why I'd recommend keeping yours as long as you keep your 60D around. If I didn't have it, I would probably be looking for an ultra wide but since I do, I'm quite happy with the 15mm field of view on a crop camera.
Or... As I am starting to lean towards... Get a 24 IS and have the same perspective on a full frame body as 15mm on crop, 2/3 of a stop faster, and a lot less distortion. The kicker is that selling the 15-85 will pay for about 80% of the 24 IS. I am having trouble justifying keeping the 15-85. The one thing I keep coming back to is the 60D/15-85 as a 'keep it in the car' kit, something I can always have with me.
I am almost certain I don't need a 24-something zoom for my 6D either. Once I get the 50, I'll shoot it only with primes for a while and see how that goes. I am becoming quite attached to larger apertures.


