I have cpu-z on and when I didn't even mess around with the stock i7 920 I was getting 48 C on realtemp. I then went into bios and barely touched the multiplier from 12 to 15, then 134 mhz to 140mhz. Now I'm at 67 C? WTF. Even at stock, 48 C shouldn't be that high.
On cpu-z it says core speed 1683.8 MHz. And real temp is showing 67 C WTF?
I'm using arctic cooling freezer 7 pro...I need help guys..
How much thermal paste did you use? And are you sure you have adequate airflow in your case?
Otherwise, I wouldn't be too surprised if your Arctic Cooling Freezer 7 Pro can't handle the i7 920's heat, a Q6600 with a lower TDP of 105W overclocked to 3.0 GHz managed to get to 89°C load in one review.
As for the 1638.8 MHz reading, Intel SpeedStep might be on reducing the core speed, but 67°C idle @ 1638.8 MHz is pretty high.
I have a Cooler Master V8 with Artic Silver 5 with an i7 920 D0 on stock speed (2.67Ghz) and I idle at 24-26C during winter (when ambient temps are lower) and idle between 28-32C during summer. Under load, on prime 95, I usually don't go past 50C. V8 is pretty heavy/big but it does its Job. I think its a bit over priced, but It's really good.
If you are planning to keep it running at stock speeds, the Intel heatsink should be fine if properly seated (the brackets MRFS linked to seem like a good idea to insure contact).
If you will be overclocking - and that chip is great for oc'ing!, you should pick up an aftermarket cooler. The Noctua listed in the above post is one of the best air-cooling units if it will fit in your case and you can afford $90.