Yep, I have an i7-3770k and at idle I have about 10 deg C variation, under load it evens out to within a few degrees C (~3-4 C). Funny part is, the "Hottest" idle core is the "Coolest" load core. I tried re-seating my first heatsink twice (hyper 212+) with no discernible difference. I changed the TIM and even bought a new heatsink (NH-D14) and it lowered the temps overall, but still had the same variation.
I know there should be some temperature variation but I thought this was a bit much (the cores on my old AMD 965 were normally within 1-2 deg C of each other). After searching the internet, and debating returning my CPU, it seems like this is normal, and probably related to the fact Intel used cheap TIM paste instead of solder under the heatsink spreader.