Re: Experience / Difficulty
While higher player settings give you more experience, it's probably not ideal to go /players 8 the whole way. If I'm not doing single pass, I usually drop it down to /players 5 after the den of evil because /players 8 can be ridiculously slow. You won't get as much experience per area, but you'll probably get more experience per hour.
I agree with this. For me, trying to get through Normal as quickly as reasonably possible, 1-hit kills is more useful than the extra experience you gain from a higher setting.
I have some really nice twinking items for the early-game, so I can make it until about the Arcane Sanctuary with 1-hit KO's on /players8 with pretty much any character, which puts me around level 22-24. At that point I usually drop to /players3 until the start of Act4, then /players1 until Eldritch or Pindle or Baal (where I may do a few /players8 runs).
I might loose a little of that time doing an extra /p8 Baal run or two to make up some of that experience before entering NM, but by the time I get there I'm ~level35 and my skills/items are starting to pick up speed & power, so I can jump back to a higher setting and keep my speed up quite well, and Baal runs give really good experience up until about level47 (you can go a lot higher on Normal Baal though, if you want to - I often push to level50 for The Cat's Eye).
For Nightmare it depends a lot on the character's power & safety, but generally I try to keep the killing speed up and make up any lagging experience in Act5. At worst I'll do most of NM on /players3, but with more powerful charcters I'll go with p5 or p7 until about Act3 (when the experience gained on higher settings and the kill speed both start to slow down a little more). Usually there's an item I want around level75 (Reaper's Toll, Dracul's Grasp, Kira's Guardian, Griffon's Eye, etc.) so I'm seldom lower than that before entering hell. I don't go past level77 in NM though, and I don't remember ever entering hell with a character still in its 60's, except maybe a sorc or two meant to teleport past as much of the game as possible and go straight to an MF target.
When I enter Hell (and the /players setting) really depends on the character I'm playing. If I want to push for a higher level for a certain item early on (Arachnid's Mesh, Stormlash) I'll do some Countess or Pits runs.
