For what it's worth, anything posted on the internet in small size, heck even 100% won't really give you an answer you're searching for.
But.
I work in a professional scanning business, I run about 7 Epson v700s for most consumer ****, people digitizing their dad's or mom's album, negs, slides etc. And it's fine up to 2400 dpi. It all gets edited later anyway. Once in a while we get a major client like a gallery, artist or photographer who request 4000dpi scans of the ****tiest slides they bring you.

So, I got the boss to buy a true film scanner, a Nikon Coolscan V. Almost the same as 5000 minus the multipass option and whole roll adapter.
Being as it may, I did a lot of tests among the coolscan and the epson v700. I tried slides, i tried kodachromes, i tried negative colour and bw. Obviously I scanned the same photo on both with the exact same settings using vuescan. My main goal was to see which has a difference in sharpness or detail. Well, what do you know, Coolscan blew the epson out of the water with incredible amount of detail, whereas Epson at 4000 dpi is mush. Having said that, the coolscan provides extremely grainy scans, so beware.
If you decide you want high quality results on you web portfolio under 1000 bucks then your only choice is to go double scanner. You get an Epson V600 or V700 for your medium format, and a dedicated film scanner for 135, like Coolscan V/5000 or Minolta dimage 5400. Or any of those useless Opticfilm what have you that take forever. (Tried one of the pacificImage high end ones). The truth is, your web visitors won't give a **** about detail, they will want to see good pictures (usually small anyway). For my personal stuff I use an Epson V600 for 120 and work's Coolscan for 135. So there you go. Unless they produce a multiformat scanner for 120 and 135 under 1k soon, you're screwed. Oh, or do digital camera scans... :bang: