"Cooling" is largely a meme and I'd wager best case scenario would be no difference than 10% difference.
The larger cone (possibly latest model?) SA series are 2 3/4" coil, the 2.5" coil ones on their site are sill only claiming 750W power handling. I've spoken with Jacob at length about how "power handling" should be defined and at least some years back when we spoke he and I were in agreement there. I would generally consider Sundown ratings to be very honest, and I've only seen perhaps one or two that seemed optimistic but I'd reserve judgement until I could test for myself. OR to put another way, anybody selling a sub with similar coil to a Sundown product with a higher power rating is exaggerating.
That aside, the "rule of thumb" with this sort of thing has generally been 100W X coil diameter in inches X number of layers is going to be your continuous thermal power handling. That comes second from the engineers at Eminence which is a reputable source IMO. Of course that doesn't account for if you have say an underhung woofer with 1/2" wind width coil or similar that probably won't hold true, but it's a good ballpark and I find it very accurate in predicting true long term thermal capacity of coils in modern high powered subwoofers.