I've never had any of these issues, but not saying it can't happen in a hotter climate.
I've tried tons of different sabot/bullet combinations in a couple different Knight rifles as well as my CVA and had virtually the same experience on paper with 90 grains of BH. I've done the harvester crush sabots with different bullets, and while easier to load, accuracy wasn't significantly different. The Barnes T-EZ are good bullets and fairly easy to load and have killed well in the past. For better long range performance and expansion, I've used the Precision Rifle bullets out of Canada. Their all lead 260 grain extreme elite and QT Polymer tipped are excellent bullets and leave big holes.
2 years ago I was out of bullets and picked up the 250 Hornady SST the day before late season opener, because that is all the Scheels had left. To my surprise they shot as good if not better than everything else i've tried. They also loaded very slick, and I've shot up to 10 times without running a patch or scrubbing the barrel.
One thing to note on bullet weights. The heavier you go the tighter they fit with sabots, so you need to pay attention to this. After 4 or 5 shots a 300 grain sabot is gonna be more difficult to load than a 250.
I haven't used black powder, Goex, pyrodex, or Triple 7 in years due to the filthy, nasty, corrosive mess they all are. I had 2 Triple 7 pellets turn to soup overnight when I brought a cold gun into a 60 degree basement in a case!
Blackhorn is a game changer for cleaning and can easily be cleaned out of your barrel with hot water and dish soap.