is the arctic MX-2 good for the thermal paste?
Well, yes! But Arctic Silver is better but somewhat hard to work with and takes up to 200hrs of "burn-in" before it performes at it´s best! MX-2 will do!
What temps do you have on the CPU and more importantly what CPU-Cooler do you use.? Not stock i hope....
Regarding that heavy usage would slow the CPU down i´m sceptical! It´s often due to other stuff like sw conflicts, slow HDD´s, botllenecks, temp issues etc. My experience is that either a cpu work or it doesn´t!!
Also how big is your chassis and are there enough chassifans? Are all wireing out of the way so you get a good airflow? There are numerous thing to weigh in when temp-issues are a problem.
Changing thermalpaste is usually not the first thing to du unless you are unsure if there´s too little or too much of it!
If you have the money a GTX 1060 or AMD 480 would give your comp a good boosting! An SSD is also a GREAT investment to speed a comp up......