wider L zooms aren't so great on crops imho and offer not usually desirable focal lengths but YMMV. I say look into the medium telephoto primes. 100L Macro, 135 f/2. Now those are lenses that shine on all bodies.
Odds are the next 50 will follow in the 24/28/35 path and will have IS and a slower Aperture. I am betting 50mm 1.8 or f/2 IS at $749.00 in Fall or Spring. Will it be 4 stops? I personally would love a handheldable 1/20 1.8 with true ring USM but how much am I will to pay for it? I think this is a job for Sigma, not Canon.
I've sold two! I sold the first for 150 more than I bought it for and the 2nd I 'gave it away' for 100 less than I bought it for to a dear friend on a budget. She's happy so so am I. Tamron 24-70 VR was what I replaced it with. SOOOOOOOOO much better in every way.
I use Purosol as well with Pecpads. I follow up with an Ilford antistatic cloth. I had a 135 f/2 front element which had horrible goo specks and I couldn't get them off and was worried about the coating but I just kept doing light applications 4 or 5 times and finally cleaned up nicely. For dust I use a Rocket Blower and gravity.