I'm probably wrong, but wouldn't it be a decrease in overall productivity? 2.2x increase in speed (higher the better) but ~7x increase in load (lower the better) for the same workload.
Or let x be time we need to complete the task:
12.5 * x first (load over time) is less than second 100 * x / 2.2 for the same x.
Yeah, it depends. How much memory bandwidth do you use with each? Are the results useful incrementally? What else do you have to do on the machine? If this is the only task, and you don't care about power use, then using all resources for a quicker time is better. If you care about power use, or have other things running on the machine, then great. Being in place will of course matter with memory bandwidth and available RAM.
Or let x be time we need to complete the task:
12.5 * x first (load over time) is less than second 100 * x / 2.2 for the same x.
Or is this an inaccurate comparison?