An M52B28 with just an M50 manifold/remap decent ratio diff, will give an E36 M3 3L a fright up till about 120, a stripped out lightweight e30 will be neck and neck the whole way - seen it for myself.
An S54 will require dedication if you intend to drive it hard as intended with a high revving ///M engine.
Ideally source an engine with proof of the crank being reground/polished, and someone that doesn't mind chucking it on an engine stand and taking the sump off for you to inspect it, anyone with nothing to hide that breaks bmw's wont have an issue doing this - only someone with something to hide.
If not and you buy an unopened engine, you WILL end up with a shagged crank/bearings, as with any ///M engine, it's just what they all do. Me and my mates have been breaking them up for parts for many years/building various bmws, and my mate rebuilds engines, he's had to often buy multiple cars/engines just to get 1 good crank, regardless of the mileage/history, the last time was with his S50B30, I think he ended up buying 4 engines to get 1 good crank.
Another of my mates bought a brand new S54 crank from BMW 10 years ago, it was IIRC £5600, and I doubt they'll even sell you one these days.
Bearings wise, if you use oem bearings, you will get more life out of them, circa around 30-40k, but they run the risk of killing the crank under abuse, if you go for ARP, you'll have to replace them every 10k due to being race parts, but they won't take the crank with them if they die. Obviously your mileage will vary depending on how hard you drive it, but an ///M engine is wasted if not used for it's intended purpose.
Regardless they all kill cranks, don't believe anyone who tells you otherwise, they've either never inspected it or the bearings, or bought a car/engine that's had the work recently done then not driven/owned it long enough before it needs to be done again.
You'll also want to do the valve clearances every 10-15k, as long as you don't mind doing this and the ARP bearings yourself or know people, then it's worth it, it's just the same with any ///M engine, they love to murder a crankshaft/shag the bearings and all require the valve clearances doing frequently due to the type of high revvy race derived engine that they are.
Either way it's worth the faff if you're going to keep the car and drive it hard/track/drift it.
However an M50/M52 will just work and take a kick in everyday and you'll never have to worry about the crank or bearings, I've had 5 E36's and never had an issue, the last one being a ridiculous spec M52B28/custom rebuilt 3L M3 LSD swapped coupe with stupid amounts done along with tuning. It got it's head kicked in everytime it was driven, zero issues over 5 years of constant abuse spanning over 130k miles of use along with drifting it whilst living on the limiter. Zero issues. Only thing that kills a M52 is if you don't bleed them properly and cook them, due to being an ally block, this is easily done if it's been done before when it comes to bleeding them yourself when you're for example replacing a stat/waterpump/rad/hose. The best way is to lift the front of the car up if it's being a pain.
You'll also want to get a proper plated LSD and rebuild it - a good option is to use double the amount of dog and friction plates, or just use thicker plates, whatever you prefer. My M3 diff ended up being 60% lock 1.5way with 4 thicker plates + all the bearings/seals/top hat bolts etc etc, locked up amazing and was awesome for daily road use along with if you wanted to drift it or track it. Just find someone you trust to setup the ramp angle properly.
My mate built a S62B50 E30 coupe, everything custom, E34 M5 box and diff/custom rear end the lot, even runs posh waterless coolant, spins all the gears even at half throttle on semi slicks haha, it's hilarious fun and stupid fast, he's made it close to 400bhp per tonne, so it will destroy any bar a R35 GTR/exotic power to weight wise.
On slicks it will destroy basically anything as I say power to weight/response/handling, and drifting it is amazing too.
