Does the bike run good with the 270's in the summer? Maybe its lean because its cold here still.
270-280 should be really really close. My buddy with CPI's, Pod Filters, and Cool Head runs 280's in the summer. To give you an idea my aggressive dune port, CPI's, Vforce 3's, pods, +4 Timing.....etc runs 310 mains in the summer with needle second notch from blunt end. So I would imagine you would be a few sizes smaller than me with stock porting.
I would leave the needles on the second notch from the top, and throw your 280's back in, or even some 290's wouldn't hurt. Oil on the end caps is normal, mine does it too. I'd rather be a little rich than too lean.
-Zach