Not too sure, so I didn't want to give an answer right away.
They might even do well to be separate statistics, something like DPS vs KO Time. As in, you'd find both the maximum possible area covered if every single one of your shots inks new ground, simply calculated by Ground Covered per Shot x Fire Rate (I think I would average ~10 shots to find that value) as well as the "actual" coverage in a given time period. As you've said, the optimal best case doesn't paint a realistic picture of how the guns may actually perform in a live match. The problem is you can't really determine what a realistic setting may be, as all maps have a combination of flat open areas, turns and inclines, walls/grates/uninkable surfaces, or anything else that might make your gun perform better or worse than average.
I suppose the ideal situation would be if a member of the opposing team using the exact same weapon was matching your shots 1:1 right in front of you. That, or you have perfect control and accuracy to maximize the efficiency of your weapon.
Step back and think how this information would be used, and what people might want to know in order to compare the weapons and make informed choices on their desired loadouts. Players won't always be continuously firing their guns, overlapping shots on their own ink and wasting time, so testing ink coverage by walking and shooting in a straight line isn't a helpful statistic. But you can't exactly test the typical jump/shoot/swim combo, as that's a tactic to maximize distance covered and ground inked over an extended period by conserving ink, and not the true potential of their gun in any given second.
So do you want to know the unachievable absolute maximum potential of your gun, to know how it fares in quick bursts, or do you want to know how much of the map you'll cover throughout the course of a live Turf War? Revisiting DPS vs KO Time, nobody thinks they can kill 5 enemies every second with a .52 Gal, that's not what that number is saying at all. It's just that, when the opportunity arises, you can win a 1v1 fight faster than any other gun. That's what people want to know, not some "realistic" KDR potential with all sorts of variables factored in, although DPS does give you a general idea.
The complex stuff is best suited to charts and calculations between hard stats, so don't try to incorporate that into the raw data. Accuracy, fire rate, ink efficiency, and movement penalties will affect your "actual" ground coverage, so if you attempt to find a "realistic" inking potential in order to prevent faster/accurate guns from appearing better than they really are, players might doubly account for that and consider them worse than they really are. At least that's what I think.
Oh, also you can jump into an empty "real" stage if it's currently in rotation, but you'd have to do all your testing right there before they swap, and only if it's a relatively good map for testing in the first place. Gives you some more space without a team to worry about.
