I just installed an H80i water cooler on my 3770K. Currently with not much load my 3rd core is sitting lower than the average(10degC less). Is this normal or is this a result of noobish thermal comp application?
Don't worry about it much. Ivy Bridge is well known to have some issues as far as temperature accuracy is concerned. It's because the thermal compound that Intel put between the chip itself and the heat spreader wasn't applied evenly. That's why there is a fair share of people who "de-lid" their IB's to re-apply thermal compound (and in this generation Intel just glued the heat spreader on, previously they had soldered it on (I'm not a expert, someone will have to confirm. This is just what I've heard.)
Long and short, don't worry too much about it. There isn't much you can do. Just know to look at the hottest core (that's what I do) and just remember at lower temps, it's pretty inaccurate.