Speed Fan Vs Core Temp?

I have an Intel i7 920. I'm getting 26-28C on idle in Speed Fan, and 41-43C in Core Temp. What gives? Which one do I believe? I'm not familiar with temp utilities, but you would think they would be closer. I'm considering getting a new CPU fan if that's the case. Load temps get at 87C on Core temp. I'll post what speed fan is later as I do not know.

Thanks alot!

Core i7 contains Tjunctio Target in one of its Model-Specific Registers. This is software-readable and most programs will retrieve this when they detect an i7 instead of using a pre-defined Tj Max like with Core 2. Speedfan doesn't yet do this and defaults to about 85C for Tj Max (not exactly sure what it is). If you want to use Speedfan then simply run Core Temp along side it and adjust the offsets for each DTS until they read the same. You can read how to configure the offsets in Section 11 of the Core 2 and Core i7 Temperature Guide. I think Speedfan still has trouble with Hyperthreading and will show up 8 core temperatures in pairs of identical readings. You can use the configuration to disable the unneeded ones and rename them properly. Core 0, 2, 4 and 6 are the only ones you need to look at and can be renamed to Core 0, 1, 2 and 3 once you disable the others.