Quote:
For the record, I have the EF 75-300mm f/4.0-5.6 IS and want the EF 70-300mm f/4.5-5.6 DO IS USM

For the cost of the latter lens, I'd imagine you'd just want to go it a step further and get the 70-200mm f/2.8 ($1500, more or less, from both Canon and Nikon, with a similar feature set of bells and whistles) plus maybe a 1.4x teleconverter. Either lens would look quite pretty on your shelf when you leave it behind because it's too heavy to lug around.