After many trials and viewings on different screens, I have finally decided to put my shows at 900x600 with no 'fit to screen' option. I have noticed that some screens do not have the best quality in the angles or along the edges, others aren't correctly adjusted by their owners (lateral or vertical shifts, pin-cushioning, barrel distortion, etc.). When projected on a traditional screen, it happens not so rarely that the edges of the screen are curved (curled?). With this size (I use 900x600 because it is the correct ratio for 35 mm film as some of my pictures come from slides), which may sound odd at first, I'm sure that the pictures will display at their best in the center of the screen where the quality is best. And even on my 22" monitor at 1280x1024, this size isn't ridiculous (I also use a dark background image to enhance the main image). Finally, this size gives the opportunity not to compress too much the original picture, thus having a good quality, and still keep the show at a reasonable weight.