Just my experience, I used to race a sidecar in the early 80's, initially an a65 with an a10 crank to give 750. End fed engine, lasted 2 seasons before it was sold. Replaced with a good A65 motor, end fed (Devimead) and tuned well. Fitted with a cast iron oil pump. Reved to 9000 give or take on the cable driven tacho. Used a lot and never had a problem. Same bottom end was treated to a Devimead short 750 conversion, A70 crank and corillo rods. 840cc, Pulled like a train for a season, till the barrels lifted on the long straight at Snetterton. Bottom end was fine, except wrecked barrels, pistons and rods., We did put oil filters on each motor as well.
Properly done, the bottom end is pretty tough.
Speaking to my local engineering company (T and L Engineering, near Bedford, who have done these conversions) they comment that for normal road use, the plain bush is fine if done properly and the roller bearing is something that gives you peace of mind.
My A10 motor had them sort out the bush and crank end float.
No definative answer, but suspect its how just how it fits in your head. If I was building the motor from scratch, I suspect I would opt for the conversion, but with mine newly done, its a case of riding it and regular oil changes.
Need to investigate the fitting of an oil filter on mine though, Imagine that this addition would increase engine life.