Sell your glass a week after you get it if there is a better piece in it's league, that way you can always tell yourself you tried the lower end model and was not happy with it so you had an exscuse to buy the more expensive one.
(Just playing.)
Ive already upgraded all my glass once except for 1 the Bigma. I have gone through about 5 lens in the last year. 18-55 55-200 50F1.8 Sigma 24-70 Canon 70-200 F4 and 1 20D


Went for the 24-105 as a test to see what it was like, also it was a straight swap with no cash comming out of my Bank account which made my wife very happy.
