My "philosophy" regarding wheels is this. Plastic axle wheel sets, (proto, Kadee) goes into plastic trucks. Metal axle wheelsets, (Intermountain, Jaybee) goes into metal trucks. Metal axles will wear down a plastic truck quickly, if used heavily.
Our club puts on a major show from November through January every year, with trains running 7 days a week, 8-12 hours a day. The metal axles wore through the plastic trucks quickly during several shows, and about 25 sets of trucks had to be replaced during those shows.
I run my trains very often and I've never had the problem with the wheels wearing through the truck except for this one car where it was severely overweight. I removed some of the weight, replaced the trucks, and it hasn't had a problem since.
Metal on metal can cause problems if not lubricated. The metal truck journals can be imperfect.
I run my cars at the club pretty often. Are your cars are a bit on the heavy side?
I put this hopper wheel InterMountain. That's only if I should choose the right size?
what size set - 33 or 36?