That machine runs for 2x7 for almost 2 years now.... It can run faster but for its application i need it to last longer. No need for new case the old case works just fine. In my situation The $3.99 solution work. It's worth trying before spending the money.
To be honest my first reaction to this post is change the case....But i remember i was on the same boat 2 years ago.
If it does not address the problem sure get a new case with 120mm fan.
I see no reason for it not to work for H50. There is only standard dimension for 120mm and 80mm fans right? Give it shot before you spend your $ for another case.
There's nothing to loss in trying(may be$3.99). I expect it to work. XaserIII is a lot better than my old Antec Performance(TX) with 80mm fans. MY OC CPU temp @ prime-95(100% CPU) peaks at 56C with an average of 45C for 10 hrs. Q6600 consumes more power than your CPU.