mid-2015 MBP, 16GB, upgraded from 2.5 to 2.8 model. Benchmarks are almost the same, even worse for the 2.8 in some tests

Any thoughts on why this would be? I migrated everything at power-on on the new mac after formatting its Samsung EVO 970 plus, so they have identical drive contents and OS. Also, the 2.8 gets hot quickly (during use it hovers at around 50 or 60 degrees, where the 2.5 sits around 30) and the fan comes on loudly. Running Mojave.

RESULTS

SINGLE CORE SCORE

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4870HQ 2500 MHz (4 cores): 895

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4980HQ 2800 MHz (4 cores): 965

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4980HQ 2800 MHz (4 cores) AFTER PASTE REPLACEMENT: 962

MULTI CORE SCORE

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4870HQ 2500 MHz (4 cores): 3605

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4980HQ 2800 MHz (4 cores): 3382

MacBook Pro (15-inch Retina Mid 2015) Intel Core i7-4980HQ 2800 MHz (4 cores) AFTER PASTE REPLACEMENT: 3519

Solution 1:

Have Intel Power Gadget running while benchmarking, and watch the temperature and frequency charts on both macs. If your 2.8Ghz Mac has cooling issues (poor airflow due to dust build-up, bad/failed thermal interface between chips and cooling system) then you'll probably the clockspeed (frequency) drop under load to keep temps under control.