I hear people's catastrophic problems they have with there Chinese built engines.I know there metals don't compare to ours or other countries- China does NOT put enough carbon in there metals and it is very soft.I guess I have been lucky with my Lifan 1 down 3 up which is what people seem to complain about.I ran mine normal,and wide open daily for a year with NO issues,when I hammered the gears it did make a chatter sound,so I didn't blast wide open when shifting,get into gear then hammer on it.NEXT is my YX 140 which is about the same as a Pitster or Loncin.I can blast this motor as hard as I want with no chattering or nothing between gear.I ONLY use Valvoline 4 stroke motorcycle oil with a 50/50 mix of 20W50 and 10W40 and change it ever 200 miles- YEP every 200 miles,oil is cheap- motors and parts are NOT...I do run it hard,but NOT all the time,only for a few miles then about 35 mph.Nothing last very long running it wide open,not even a Honda.I bought my China engines because I couldn't buy a Honda stroker anywhere I looked 3 years ago.
It's not where they're built, it's to what spec...which translates into cost. Transmissions are expensive to do right, precision tolerances, quality heat-treating and top quality alloys all cost; that's where a big chunk of the cost reductions are made. Chinese manufacturers have no more magic than those of any other country, although they're basically exempt from copyright & patent law.
Running at WOT doesn't necessarily translate into anything specific, by itself. As long as peak temperatures and rpm are kept within mechanical limits, an "unstressed" motorcycle engine should be able to run like this until the tank runs dry, or it's time to change the oil. FYI, OEMs do extended WOT cycles as part of their durability testing programs. It's when engines are tuned for higher-than-stock output, or a design is cost-reduced too much, that WOT operation becomes an issue. You could run a stock 49cc or 72cc Honda motor with the throttle held wide-open, no problem, as long as everything is in good mechanical condition and the gearing is matched to engine power. OTOH, racing, bang-shifting, abuse and neglect are what shorten engine life. Race engines don't wear out, they break. Say, for example, that your L110 motor can reach the high 50s, at WOT; now, stab-in a high-compression piston, high-rpm cam grind, do some port work, etc...after which it can sustain 60mph at less than WOT. 3 guesses what will happen to longevity, especially if you push it to higher sustained speeds than were possible before the tuning work. FWIW, I agree with your oil change schedule; it is cheap insurance. For on-road use, I change oil at 200-400 mile intervals, depend upon conditions.
If you've not done so already, read through the "Chinese engine mileage log" thread. There are very few entries beyond 5000 miles and the ones that are there don't paint a pretty picture beyond that level. For most, 5000 miles is likely a high number. Usually, I see guys referring to 1000-1500 as "high mileage". If this applies to you, then longevity is unlikely to be a problem...especially with your oil change frequency.
Haven't seen many L110s with the 1D/3U shift pattern in recent years. The weak points, from the era when they were the predominant flavor: clutch dampers (they're rubber, in place of springs) shift forks, gears, bearings (especially the needle bearings on the mainshaft), crankshafts. I've autopsied a handful that had been spewing oil after 5000-6000 miles. The valves, rings, cylinder and piston were typically holding up okay...not too surprising, since specific output was on a the conservative side. I noticed a lot of loose bearings; the rod (big end) and cam bearings were the shockers....that's most likely related to metallurgy. To be fair, they hadn't failed. Shift fork wear was significant, again, metallurgy. The real mystery is why the gaskets stopped sealing. It's been at least a half-dozen years since the last one left my bench. I've no idea what has changed since then