I'm a growing fan of E type mechs and have used them on my 2 latest builds. For what it's worth, some observations...
1. Expensive XT mech looked nice, but cheapo Altus job actually came with a stiffer mounting plate and rices a better shift.
2. I've used a standard BB each time, but I've been careful to make sure that I've bought BBs with a good fat lip on the drive side. No problems.
3. Not that I've had any slippage problems, but be used a dribble of Loctite Blue on the mating faces.
Good luck.