Glass or Body?

I have a 20D and I was planning to buy a 300mm f/4 IS in the very near future. At least until I saw the rumored rebates for later next month. Assuming the info is accurate ($300 for a 5D Body and $50 for 300 f/4 IS) what would you do if faced with this decision? Full-frame is VERY tempting but I guess I can always upgrade down the road.

Thanks.

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Kevin Bryner

http://www.kevinbryner.com