So I am pretty close to buying a 40d right now and wanted to get the 24-70mm 2.8 L lens to go with it (and hopefully a few other "L's" to come along a little later) until someone on a different forum suggested it wouldn't match up well since its not a full frame sensor on the 40d. Is that true? They suggested I look at a 17-55mm f2.8 EF-S instead. Obviously I would rather have a 5d or even a Mark II but I'm getting a really good price on the 40d which is helping me to afford the 24-70. Is it worth me spending over $1000 on a used 5d just to be able to get the 24-70? I'm confused as hell right now. Help!