ORIGINAL: DarZeelon
In normal circumstances, as a sport engine, this is true.
But if put under best effort condition, such as sport Quickie racing, they are just over-stressed and fail (see Vicman's post and I have seen several locally).
We've only seen one TT46Pro bust up an "original" rear bearing and it was doing about 17K RPMs at the time. Surprisingly one of the balls exited the engine (goodness knows how) and although a few fragments of the bearing cage made it up into the top of the cylinder they did so without scratching the bore.
The piston was slightly scored but we simply replaced the bearing and ran it *very* hot and hard with some 20% castor fuel to varnish-up the score marks.
That engine still runs "good as new" today, several gallons of (better) fuel later.
It is not the ABN P+L that I have seen peel like in some older OS FX engines, but after a few very high RPM runs, they no longer hand-start and power is down significantly.
Using the oil we all know about, we regularly run our TT46Pro engines at 15K-16K and have noticed no wear. Perhaps this is below the "critical RPMs" that cause the wear you speak of. Ours are also largely uncowled so they get very good cooling that probably helps a lot.
Unlike another 'inexpensive' offer from an after-market source that sells his high-speed sets for no less than $36 minus change, [link=http://www.mcintoshcentral.com/rc-bearings/catalog/product_info.php?cPath=81_87_102&products_id=713&osCsid=c0cdae6bd775751c872cc27f372de4d1]Paul of RC-Bearings[/link] offers his set that includes a rear bearing ONLY with this protective, non-metallic cage, for less than $7 + shipping.
Yep, I noticed that the last lot of 46-sized bearings I got from Paul had non-metalic bearing cages -- maybe that's also why our engines are standing up so well to date. I bought a bunch of bearings when we changed oil because I wanted to start testing from a known-point. After that initial retrofit we haven't had to change any yet so I've still got a box-full here.