The Thermaltake S21 did not preform very well under high load, and I think it mostly has to do with the lack of cable management. Yes, in a smaller case you are going to see an increase in temperatures, but the enemy is often just cables blocking air flow, and this appears to be what happened here. The lack of support for a top mounted fan didn`t help either. Even so, I like to test my cases out as stock, but having the option would lead me to try an extra fan that could potentially lower temperatures. Even though I haven`t found a way to properly measure how long it takes temps to drop from load to normal idle, my observation simply concludes that it would take a very long time. Air was getting trapped in the top corner, and I could feel the warmth. Are the temps really out of the realm of normal? No, and I`ve used cases that are far worse."
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips