Upload & Sell: Off
For me ... it is the same as LR 4.1. Loading (starting the app) seems to take a little longer, but once it is loaded, I can move in LOOPE mode or DEVELOP mode pretty much the same as it did in LR 4.1.
Did you defrag your HD after you upgraded to LR 4.2? I just did a file-level defrag of just the "C:\Program Files" folder and it seems to be peppier today (or it could be a placebo effect).