I started a seasonal wizard just to get going. Is a barb or crusader smoother to bot with? I can't tell what the bot handles best. I know DH is good, but I think wizard has more range. I never focus on pushing grifts just speed until I'm geared and legendary gems are leveled.
Before the season started I experimented with Wizards, my favorite class, using 6p Tal's and I noticed the bot doesn't consistently use the skills enough to keep the buffs/resistances/meteor's rolling. Until an optimized skill set for Wizard appears and someone adjusts Trinity to perform using those skills properly, it will be a little random.
My proposed set-up strictly for botting would be (If I was solo playing by hand this is also the build I would use.):
http://us.battle.net/d3/en/calculator/wizard#WYfihc!RhZW!aZccZZ
It's a melee wizard with a focus on Mammoth Hydra and aspd for breakpoints. The skill choices are there so that the fire blades casting and buffs are uninterrupted.
Helm:Tal
Shoulder: Leoric (revive chance)/Aughild (dmg reduction)
Amulet: Tal
Chest: Tal
Gloves: Tasker and Theo
Wrist: Lacuni (aspd) / Parthenon (dmg reduction)/ Aughild (dmg reduction)
Belt: Tal
Pants: Tal
Boots: Nilfer for meteor damage
Ring 1: Unity for survival
Ring 2: Halo of Arlyse for survival
Weapon: Serpent for 2 hydras
Off-Hand: Tal
This is similar to what Jaetch used for 65 4p grift but for botting purposes we focus on survival because the bot is not perfect. You can find Jaetch's thread in the D3 wizard forums.
How much exp per hour? I didn't have all the pieces but 2.5 billion xp/h was possible expect lower around 2 billion. With all the gear maybe 3 billion+.
How high of a grift? With poor gear I capped off at about 36 possibly higher with luck.