My hands get sore and occasionally numb, but my forearms never bothered me. Maybe there is something wrong with my arms.
I only use a Marsh Guard in summer because it helps keep my stanchions a bit cleaner.
The RRP plastic is pretty similar to the Mudhugger and I reckon it will be as durable.
Some like a 27.5+ rear, 29 front combo. I know one rider on this and he loves the extra cush in the rear. I tried it for one ride, it felt a little odd and I could not stop worrying that I had more traction out back than the front. I feel that a regular 27.5 on the rear is not going to roll over chunk as well and ride a bit rougher. No idea how it would affect handling.
If cost was not a concern I would not be concerned with the price of replacement parts either. I would probably do it because it never needs cables or adjustment. I just changed the derailleur and shift cable on my FS bike and have had it with moronic internal cable routing. My bike isn't that bad compared to some of the shit shows out there.
Over the last few years I have gone from riding the recommended medium to large frames. Once on the same model frame. I feel more stable and comfortable descending. Cornering is just as good or a hair better. With my feet further away from my hands I can lean over the front end without feeling that OTB is imminent. It is probably to do with my shorter legs, longer torso and, arms. I have not seen a downside. If I listened to the majority of riders and shop people I would still be on a medium. I suggest trying both sizes with the correct stem and careful setup.