Different levels of boosts? A program like Prime95 will use all cores, so the cpu will limit boost amounts. Single/dual core turbo is 3.9GHz, 3 core is 3.8GHz and 4th core is 3.7GHz. But using task manager or another single number reader is only going to show the 3.9GHz number. In reality, your cores are 3.9/3.9/3.8/3.7 GHz. With an active 400MHz Ivy-Bridge boost, you'll add 0.4GHz to those numbers, in windows, but in bios (where some programs get their info) they'll read different.
As long as your temps are fine, there's no need to downclock or even worry about actual speeds. Base speed of 3.4GHz is almost never used, is basically a pointless number. You'll spend all your time at either 800M/1.6G Hz idle or 3.9/4.3GHz turbo. It's really not an issue.