I have an older Epson flatbed with slide/negative backlight. I have been sufficiently happy with it that I was instrumental in a friend getting an Epson V500. I'm not sure that it will do 5 megapixels, but is plenty adequate for me. Such high-resolution scans would be VERY slow. These Epsons will handle much-less-than-perfect-exposure slides.
The software which comes with the V500 does a pretty good job on taking care of dust on slides. I wish I had that on my older Epson unit. Dust on negatives shows up as white spots, which are far more objectionable than the dark spots from dust on positives.
I thought that the V500 was a bargain at US$150 from the river people.
I scanned about 1200 slides a couple of summers ago. I could average about 20 per hour including selecting the ones I wanted from a Carousel, scanning, and naming the output file for each scan to identify the slide it contained. One slide per file.