You're right, 70% isn't a hard and fast rule but I've always personally thought that unless an item is rare and desirable etc then 70% is a safe bet.
Ultimately it's what someone's willing to pay. Personally, I saw it as an item that is readily available (not limited run or discontinued) but batches sell out quickly due to popularity.
There'll always be someone with more range, and a higher RoF. And if there's not that, it'll be one of them pesky sniper chappies dressed as a tree, or a pre-schooler hidden in a dark corner to zap you.
But the main thing is, those are the words that always precede "I'll just open the gear box" which often ends in tears - or an ever-widening opening of the wallet until you're living in a cardboard box under a bridge...
So unless you're struggling to shoot out to 40-45m (which will probably be fixable with a new hop rubber and nub, and maybe a new barrel), I'd honestly counsel you to concentrate on improving / changing your play-style so that range becomes a secondary issue. If you're static on the front line, trying to trade shots with a bunch of other guys there will always be a Long Ranger in there to spoil your fun, it's better to find a way to close the range on a flank or through smoke, or encourage some proper covering fire from your teammates so you cancel out that range advantage.
It's easier said than done, I admit, but you give yourself more chance of making a "hero moment" of breaking a deadlock. I had mine at the last skirmish when I took advantage of a well-placed smoke grenade someone else had thrown to push forward 10 yards and take out the two guys who were completely holding down the rest of my team. (I'm still waiting for my medal, it must be coming)
That's so much more satisfying than just having a gun that happens to shoot 2m further than your opponent.