Hey Loki, I think there's a few of us on here experiencing similar issues, well done for not letting it get the better of you.
I get your reasons for mag compatability etc, between rifle & pistol, but cant help but think that the benefits of the lighter carbine will be offset by the weight of the numerous gas mags you'll need to carry, especially if you want any kind of reasonable ammo capacity ?.
Obviously a dmr role puts you midway between assaulter & sniper, bit more limited on fps, & probable range, than a fully set up sniper.
Why not consider something like an m14 socom, light & not the full length rifle, but excellent range, especially if you can get it to the dmr limits (& ive heard good things about players insulating inside the body for further sound reduction), aeg so good all year round, & technically you'd probably get away with just one mag if you run a hi-cap, meaning you can slim down your load carrying kit to the bare essentials, & a well set up nbb mk23 or Nov equivalent & 2 or 3 mags should cover your sneaky sidearm needs.
Obviously im not trying to teach you to suck eggs lol, you've been at it at least 5-6 years longer than me, but being equally broken means ive had to drastically rethink what i use.
Worth considering ?