well, i think that depends on with how much force you want to attack. 300k for 3 players is 100k for each.
if i dont have calculated it wrong thats a minimum total building time of about 156 days (without building time upgrade for pearls) or 137 days (with maximum building time upgrade for pearls) for 100k rum consumption, if you only build the offensive units with the lowest building time.
that units would make a total of 7.4kk offensive force (without discovery bonus) or 10.4kk offensive force (with maximum discovery bonus) for 1 player.
otherwise, if you only take the weakest units (marauders) you will have 4kk to 5.6kk off per player, or if you take only the strongest units (juggernauts) you will have 42kk to 58.8kk off per player. and of course thats not even close to the limit, because you can still pardon your units, add some dread fleet, off enhancer and potions.
if you really want to hit it hard, you could use i.e. 1,162 plague ships with 23,257 pardoned, max discovered juggernauts,
which would give you 85.3kk off for your 100k rum consumption, and thats still without potion and off enhancer. so, i think thats more than enough to do heavy damage.
besides, its not quite easy to reach 100k rum consumption if you are always low on rum because the maximum production is
24k (from distilleries) +25% windmill +25% ruby boost = 36k and the maximum decrease rate is 10% pearls + 2*5% davy jones locker + 50% ruby boost = 70%. so you can supply a consumption of 36k/0.3=120k. but an average player may dont use the very expensive ruby boosts and dont always have rum items, so its more likely 24k*1.25/0.9=33.333k. so you already have rum problems at 1/3 of your 100k you can use for a massed attack.
compared to other plarium games, like soldiers or sparta, where are buldings which decrease consumption up to 85% (if i remember correctly),
the 25% increased production through the windmill is nearly nothing.
to make it understandable for everyone. just with buildings and pearls (because thats what everyone easily gets) ... here in pirates you can supply
4000[base production distillery]*6[distilleries]*1.25[windmill]/(1-0.1[pearls])=24,000*1.389=33,333 base consumption with lvl 20 distilleries.
in soldiers i.e. you can supply
500[base production]*6[production buildings]*1/(1-0.85[reduction building]-0.08[pearls equivalent])=3,000*14.287=42,857 base consumption with lvl 20 production building.
so you see, you can have 42,857/33,333=1.286 times more units before you are loosing consumables,
and when you are loosing consumables you still can provide 14.287/1.389=10.286 times more units with them. so you dont run out of consumables that fast.
i question myself what good a high limit is if you are having big problems to reach it.