One of the problems with the "geewhiz it's a 347" crowd is that there don't seem to be any of of them that have run 100 K miles or more. The stock EFI 302 will do 150K-200K miles with minimal problems.
The same is also true of the Gforce and other high end T5 upgrades. No one that has a GForce or other Super T5 has 50K -100K miles or more on it to see if they really do hold up.
I would put my 100K+ long mileage bets on the 327/331 combination. There is still a lot of piston skirt left compared to a 342/347piston. That extra skirt helps stabilize the piston so that it does not rock in the bore after a lot of miles and wear.
The longer skirt does provide better oil control...
Now, I would say the real reason for the 'lack of mileage' is because most stangers that put money towards stroking the bottomend and using drivetrain parts that are beefed up typically have another means of transportation.
In other words, the strokers/G-Force equipped cars are 'weekend warriors'...
They aren't going to rack up the mileage, although I think several of them could hit 100k with no issue.