In my experience, LEDs are marketed at their maximum safe overdrive, but spec'd at their most efficient output, which is much lower.
Take this guy, advertised as 10W at its hard limit of 3000ma.
But all the specs in the sheet are based on driving it at 1050ma, which yields about 3.1W. This yields 400 lumens or an impressive 129lm/w (I'm reading out of bin V2, 85C which is conservative, other bins/temps go as high as 172 lm/w).
However running at the (advertised) hard limits of 3000ma, it only gives 91 lm/w. Whoops.
So in that case you get a 41% efficiency gain by driving the device gently. It's funny, the curve doesn't look that bent! But it is multiplied by the amp-volt graph, which is bent too. Try 480ma @ 2.78V (from the amp-volt graph)... 50% rated lumens so 200lm, @1.334w or 150 lm/w. Crazy. And that's the lowest bin, if we get into the high bins, low temps and underdrive, we could hit 200lm/w.
Having looked at quite a few LEDs, this is very typical. LEDs make heat for 2 reasons: being overdriven to get max lumens from minimum $ in emitters; and phosphors are inherently inefficient.
All things being equal you are better off driving the larger device at 1/3 power.