Greetings Bugman,
I agree on the castrol GTX, not because of breakdown but its waxed based [censored] that will plaque a motor. Im shocked at hearing such good words about it for years.
Motul v300 is the same as Silkolene Pro4 as far as base oils. both Group V ester. The difference is the Motul has 3,000 ppm of calicium and near 600 PPm of moly, why does a group 5 ester base oil at $16 per quart need all those additives, and 3000 ppm of calcium when a group 5 ester is supposed to be a natural cleaner). The silkolene doesnt have all that moly, I have seen Black moly spooge in clutch baskets after running motol v300, although I never experenced any performance issue. I was replacing a cam chain and removed the clutch basket.
The key here IMO, is change interval, it makes the difference on what oil you can get away with, but I hear what your saying on transmissions. A key thing, are those who shift clutcless will be much harder on the dogs. How do you take this into account , whats oil related and shifter created? Its going to make a difference long term