The 70-300 IS is a lot cheaper than the DO version, & although slightly bigger, its lighter & no slouch in IQ terms ... then you could afford the IS macro
Check out the review at
http://www.photozone.de/canon-eos/20...report--review
Conclusion : ".....The optical performance of the new EF 70-300mm f/4-5.6 USM IS (non-DO) is simply about as good. Mechanically it isn't quite in the same league as the DO lens but ... hey - it comes at a 50% lower price tag! If we throw in the added values plus a little coolness factor the DO lens may be worth a 200-250 EUR/$ premium over the conventional lens but at 1100 EUR/US$ it is simply way over-priced"
.... and prices have gone up since that was written
