you also have to think about the differential effort required to maintain 1200 vs. 1000 cals/hr in relation to the time you would gain.
over 40 cals, a 1200 cal vs. 1000 cal is 24s gained. over a ~12:00 workout - I'd say you're better off sticking to the lower end and trying to gain time or not lose time elsewhere (esp the heavy DB, or the GHDs)