Slide Scanning 3000dpi v. 4000dpi

A few weeks ago I checked out Scancafe.com based on recommendations from a thread in here. After hours of sorting slides and emptying projector carosels I'm ready to ship my slides off. On the order form I have the option of having them scan at 3000 v. 4000dpi. Aside from the obvious, what would you consider the pros and cons of paying the estimated $80 - $160 extra for 4000dpi.

I have approximately 1500 slides, most of which I just want to have in digital format, and there may be 100 or so that I think I would want in 4000dpi. To which I am thinking I could just resubmit and have re-scanned.

So, based on your maggot opinion what are the limitations of 3000 v. 4000, and what would you do?

Do you need a 13MP image or a 24MP image?

Does scancafe do a decent enough job with the scanning for their to be an actual increase in image quality from 3000dpi to 4000dpi?

Are the images actually crisp enough to make a difference? The one thing the higher dpi will showcase is a shitty lens.

Sounds like I'll order 3000dpi, and if I want I'll send the select few back. Thanks for the tips, frankly I'm pretty stoked to digitize six years worth of photos that have been sitting in archive.

Five year old thread, I know, but jryoung, how did you make out with this? And how much did scanning 1500 slides cost you? I'm overwhelmed at my slide collection and I am considering farming out scanning...

I missed this thread originally but with that many slides it would be WAY cheaper to buy your own and then sell it. Plus you would have more control.