Let's say it takes a double rad with 3/8 id piping to keep the liquid temp at @35°C after absorbing 100w of heat from a cpu. Now make that a quad radiator, its still going to absorb 100w of cpu heat, liquid might go down to 33°C. Both scenarios, the cpu sits at 60°C. The difference comes in what's after that 100w. Take it to 150w and the double rad can't effectively absorb that additional heat, cpu climbs. The quad can easily absorb it, so cpu stays at 60°C.
Liquid coolers, either AIO or custom loops are made to absorb the additional heat while maintaining safe cpu levels. Air coolers do the opposite, dissipate as much heat as possible before it gets replaced. This is why big liquid dominates over big air at high wattage levels, the ability to absorb more generated heat. But it's also why air coolers tie or beat liquid coolers at lower levels, they are more efficient.
A cpu doesn't care at all if it's 30° or 50°. It'll run the same all day. It only cares if the cooler can transfer enough wattage to keep it under 70°. Of course none of this supposition is taking into consideration ambient temps. High ambient is murder on the air coolers Delta-T, not so much on liquid
Either way, a 6700k at high OC with SLI 1080s won't generate much in the way of thermal wattage. Actually not much at all compared to a FX-9590 at 5GHz with xfire 290x which have been run successfully for years on a single loop