Topic: Viewers' Experiences -- Larger Images Vs Smaller Images ? ?

I am working on a Tiltviewer Gallery that will have approximately 40 to 60 images.  I am considering using two different sizes for the Images, either 600 by 600 pixels, or 950 by 950 pixels.  Either is likely to be satisfactory, though I am inclined to use the larger ones, all else being equal.  Of course, all the Images in the Gallery will be the same size (either all the 600's or all the 950's)

Here is my question: Will there be a noriceable difference in the experience of those viewing the Gallery, based on this choice of image size?  For people with older / slower computers, will the 950-based Galllery be frustrating / slow?  Will the use of the 600-sized images noticeably improve the loading / viewing / handling . . . the experience of public people who view the Gallery?

I would love to post links to the two test galleries, but am still in the five-day ban on links, etc.  A bit of a bummer, thus this wordy question!!