If they work 24/7, you should get to 50% RAC in seven days.
If you're reward focused, try 4 or more projects concurrently for a week and see which are getting best magnitude on your systems.
I have bought Dell T5500 with 1x e5645 and supplied it with gtx 1060, what is my all round work horse. I have throttled boinc-cpu usage to only 30%, as with original passive only heatsink otherwise cpu goes easily to 80C. I expected Dell designed it better or I miss something.
I am not familiar with that model, but many servers and towers have airflow guides. It may be because you miss that. The enterprise towers are built differently from regular gaming towers. They usualy have big fans in the front and then guide the airflow where is needed.
My R710 does not rise over 65 even after a week of full load. The R810 does stay cooler. I guess because it has only 2 out of 4 CPUs fitted.