Just got my 5DII 
When I sell my 40D to pay for some of it, I will be missing a focal range, as I will have 17-40L and 70-200L (plus nifty fifty and BIGMOS) but no 17-85.
Buying a 24-70L or 24-100L is an option but very expensive.
My question is, if I use a TC on the 17-40L will it affect IQ by much. In other words can I get away with a TC and not another L lens at this moment in time.
Many thanks
PS. I know I will loose stops with a TC.

When I sell my 40D to pay for some of it, I will be missing a focal range, as I will have 17-40L and 70-200L (plus nifty fifty and BIGMOS) but no 17-85.
Buying a 24-70L or 24-100L is an option but very expensive.
My question is, if I use a TC on the 17-40L will it affect IQ by much. In other words can I get away with a TC and not another L lens at this moment in time.
Many thanks
PS. I know I will loose stops with a TC.