Ok first things first, for those who don't know, Star_Folder lives and breathes hop up. And hop up = range and accuracy. Very few people actually measure out to the foot how far 300 feet is. Its quite a ways for an airsoft gun. Not to mention 400. With my first DMR build I got to 275', with a m160 spring. On my second I got to about 315', with a slightly heavier spring. And that was everything maxed out other than the TLC on the hop up (don't get me wrong, I know how to install a good hop up.) But that's the difference. Star, to his credit, works some crazy magic on his hop ups. Its not something you can just pick up and get right the first time. I would tell you to expect and be happy with 275-300' of range.
The biggest difference in my two DMR builds was accuracy (pre-cocking gearbox for the win). Which is why I label them more as a DMR and a semi auto sniper rifle.
There are really 3 gun styles/styles of player involved in this discussion. The wannabe DMR, meaning full auto to the limit of FPS, the DMR, and the semi auto sniper. The priorities of the DMR and the Sniper are different; obviously, the sniper focuses on firing and staying undiscovered. The DMR is involved in the standard firefights, they generally stay in a relaxing range just outside the enemy's, pop some people who aren't paying attention, help take out one or two people who are in great cover, and end up healing a whoooooole lot of teammates. ROF is very helpful for these engagements, because if you can't keep multiple people pinned down, they'll close the gap and now you're fighting full auto with semi. I think Star will agree that's his general style of play, and I would claim we could replace his 400' of range with 275' and not much would change, except for when he encounters another DMR on the field. And he'd have to work a little harder

If you play more like the sniper, out on your own or with 1 teammate, moving slowly and silently, you can understand how every single possible foot of range and accuracy matters. If you take a shot and miss, first, pray they don't detect you, then move closer, then try again. ROF only matters when people don't call their hits because they don't think they've been hit, since they're not engaged in a firefight. The longer range you have, the harder it is to be detected.
Now, I did say I only ever got my gun to 315 feet of range. And that's because, when you're a sniper, you're generally in brush, dug in in the woods. Places where it is difficult enough to line up a 250' shot, let alone something over 300. Obviously that depends on where you are playing. But I've played my share of AOSC fields this way and am content with my maximum range.
I've been in what appears to be semi-permanent hibernation for quite a while, and thinking back on airsoft guns and games I don't really remember who's gun shot how many feet, but who was the most effective on the field. Dom has kicked my ass more than once when I was carrying a 300' range semi auto gun, and he had a P90. The tech work is fun and does create a challenge, but it does not directly translate to effectiveness on the field.