I had 600 of my parents' prized possessions: slides over a 60-year marriage. A small survey and one test batch led me to digmypics. I sent several batches to prevent any transport mishap from wiping out the entire collection. The results are wonderful. The digmypics service is very definitely all it promises, and economical.
My only complaint is that it's impossible to review scans without seeing the full resolution scan *and* the slide. There are several scans that are not sharp; some the left side is in focus but not the right, etc. These were slight defects that were not important for my purpose. If I needed superb scans on every slide, I'd need to review each carefully and send a few slides for a second round.
But again -- this is a superb service. And don't even think of doing this yourself for 600 slides. The cost to your life expectancy will far exceed the digmypics bill.