matth87, to understand how to uniformly test, accurately calibrate, and properly monitor your CPU and Core temperatures, check out the Core 2 Quad and Duo Temperature Guide:
http://www.tomshardware.com/forum/221745-29-core-quad-temperature-guide
Since C2D variants have different temperature specifications, 70c Core temperature can be HOT, or it can be SAFE, so it would be helpful if you post your rig's variables. The following is an example format:
Ambient = Room Temp
Chipset = Model
C2Q / C2D = Model
CPU Cooler = Model
Frequency = CPU Clock
Load = Test Program
Motherboard = Model
Stepping = Revision
Vcore = CPU Voltage
Also, SpeedFan 4.32 and 4.33 both assume that Tjunction MAX is 85c, which will cause C2Q's and C2D's with Tjunction MAX 100c to indicate 15c too low. If you don't mind jumping through a few registration hoops, you can download SpeedFan Beta 4.34, which correctly interprets all Core 2 processors, whether Tjunction MAX is 85c or 100c.
Additionally, your Idle temps are already quite high, so you should first use Section 9 in the Guide to "Calibrate" your temperatures to be certain of their accuracy prior to overclocking.
Comp