Thats y i got myself a 50 F1.8 to trial out the effect of using a prime lens and if i can get use to a prime...i'll most prolly invest in faster wide like F1.4 as mine is 1.6 crop body.
At the same time after shooting a few days of F1.8 in my room for my babies, i'm also worried that i'll be " spoiled " by the shutter speed allowance of F1.8 so much + the light weight.....that i'll curse and swear at the heavy weight + size of 24-70 and yet doesn't allow me shoot at a faster shutter speed if i get even the newer version of 24-70 IS espcially when i'm moving around low light indoors.....so i'm thinking....haha
if u are willing to pay almost $3k for 24-70IS...im sure u will have no problem investing in the 35L. =) light, compact and it is f/1.4L. u can consider 24 f/1.4L II too. all same price category. they produce fantastic images.