Re: quickest char to act5?
I had this debate last season, I was trying to self-rush for socket quests too. You're basically looking at a modified LLD build, since you're going to be shooting for L20~25 by the time you hit Shenk, but will have to make it "over the hump" between about 18 and 24, so thats what you should build for.
Really, A1-3 is going to be a joke with any class. Sigon's + Civerbs makes it a cakewalk with any class. There's only two "challenges" that will really slow you down. One is A4, because thats when you start feeling the burn (literally) from elemental damage (Trav/Durance 3 is basically A4 warmup, too). The other trick is getting through A3. That's going to be half your runtime right there if you dont have a way to get yourself the Travincal WP.
That basically boils things down to 3 possibilities:
Fireball sorc
Pro: Strong offense, Leaf, useful skills become available early, TP lets you skip through zones real fast, if you have the pots to chug.
Con: Least defense/resist means you'll have more trouble with bossfights. Least amount of useful uniques/RWs at this level.
Zealot
Pro: Best defense, pally shield for resists. Vigor speeds things up at 18.
Con: Slows down a lot towards the end, once Sigons+Civerbs starts to lack. Slow to start till you get Zeal.
Doubleswing Barb
Pro: Fastest offense with dual Civerbs and lots of early skills.
Con: Slowest movement rate. No shield, suffers for resists/block in A4.
I wouldnt recommend summoner because you lose SOOO much time in places like the Maggot Lair where he just has NO good options.
My suggestion would be the sorc, if you dont want to ask around for Trav WP, but if you're willing, Zealot. Zealot is a little slower, but just so easy and point-click, and benefits the most from twinking of these three.
If you get stuck in A4, remember that you can swap out and clear the path from Pandy through Chaos with a high-level fast AoE char like an orb or CL sorc, kill all the seal bosses but not D, then swap in your mule char, and then just have them run/TP through the empty zone to the end and finish off Diablo to get the quest.