I didn't vote, but I'd also start with the 265s. Remember that you have modification limitations in Stock classes, so bigger tires usually make up for other ills in a particular car's chassis design/layout.
When we autocrossed our 86 SVO, I was able to fit, and the car was faster on the 265s we were using, vs. the 245s we started with (stock tire was a 225). But on that car, there was no opportunity for camber adjustment over the stock range, so even with the top of the struts pushed fully-in towards the center of the car and the bottom of the strut-to-spindle mount pushed fully in at the top, we could only get about -1/2 deg. So, the bigger tire still put more tread on the ground in the turns, which really helped with turn-in.
So, I'd start with the 265s and see how that fits all the way around the car, then try a set of 285s when the first wears out, if you have space.