Sitting at desktop idle means jack shit, pay attention (if possible) while utilizing your CPU to see what it runs when actually being used by something like converting a dvd to mpg or playing a newer and heftier load game. Go here and download this: OCCT
http://www.ocbase.com/perestroika_en/index.php?DownloadIt has a CPU, memory, and GPU tester. Give those each a run, and get a more realistic idea of what a heavy game or processor heavy task really does to temps.
Also, your MB appears to possibly already have holes to support S775 coolers, but double check. That's another thing, the 1156 intel mount holes are different. I recommend a Xigmatec S1283 in all honesty, it competes with $80+ coolers and can usually be had around $35 these days...and it doesn't hurt to get the additional $12 1156 bolt bracket for a tighter fit. And even then it's sitll a good cooler, here are some options for ya though:
http://www.newegg.com/Product/ProductLi ... +hdt-s1283Xig S1283 and 1156 bracket assy...the bolt kit makes things easier but the MB may need removed to attatch the back support tot he mb. Boy have prices gone up on this cooler, still a top notch cooler.
http://www.newegg.com/Product/ProductLi ... 0LGA%20775An assortment compatible outta the box with 1156 socket mounting.
Even the AC Freezer 7 Pro will be much better than the stock cooler. I used to run one on my old dual core that ran pretty hot till I slapped that AC on there. And considering the stock performance levels show no need to overclock that thing yet, no need to get the biggest cooler you can find. I'd either go the AC F7P or Xig S1283, but I've had a lotta experience with both and both were fantastic, but there are quite a few other good coolers out there...for a price.