@w349: indeed weather sealing, didn't think of before but very, very useful

@neuroanatomist: when the 5D3 becomes less expensive, I'm indeed planning on buying it.

Does anyone have experience with these lenses in the field (or with both of them). I really love the IQ from the IS version II, but I can't compare it to the two lenses mentioned here, which are said to have a lower IQ. Should I be afraid I will be dissappointed or just go for it ??