I'm in a similar situation to ChrisS. I have a 40D and RZ67 with 4 lenses and teleconverter. I love the image quality of the RZ but find the workflow, weight and restricted focal lengths to be enough of a disincentive that I haven't put a roll through it for quite a while. OTOH, with three lenses (10-22, 24-105, 100-400) I have a 35mm equiv of 16-640mm (+ 1.4x extender) in a relatively lightweight, compact system with the 40D. However, I printed an image 16x24" recently and was slightly disappointed with the digital artifacts in this rainforest scene. Sharpness and other measures of IQ were fine, and I uprezzed using Bicubic smoother, output sharpened with Photokit. The shot was taken on a tripod, MLU, f/11, ISO 200 with the 10-22, so don't feel technique suffered, but the print was slightly disappointing with nose-pressed-to-glass viewing. To be completely honest with myself, my work is almost always printed in books, calendars, diaries etc. In other words, quite small, yet I'm lusting after better quality. Like ChrisS, I too have been considering my options: 5DII, 50D, haul out the RZ. I'm leaning towards the 5DII but would need to also buy the 17-40 f/4L (and 17mm T/S lens if reviews are favourable and I can convince the exchequer of the household that it's a worthwhile investment ) and would also use the 70-200 f/2.8 that I also own. While undoubtedly better image quality, it will end up costing $5000 (Australian, incl lens), be a little heavier, and be quite a bit shorter at the telephoto end. 21 full-frame megapixels just has me drooling and I am very keen to try to sell larger prints. Lots to ponder...
Andrew