I just assembled my NUC last night and still has a long way to go... will be trying to install the drivers (Driver Bundle Win7-64Bit Sep2014) this evening.
Our setups are very similar; NUC, SSD, 1 stick 8GB RAM, no BT, no wireless, no mSATA.
Seems the USB extension cable didn't actually solve the lag problem.
Have you tried the released USB3 driver "Intel(R) USB 3.0 eXtensible Host Controller: 2.5.3.34"?
Frankly, I'm very disappointed with Intel for releasing such a poorly tested product, and to think that these known issues hasn't been resolved after so long is simply appalling.
Let's hope our efforts leads us to a resolution of the problems, or I'm going to try ask Intel for refund and take back the unit.
Best wishes