OK... I just spent WAY more time than I'd like testing different wheel/rotor/brake pad setups, and it appears that all 3 can be a contributing factor to the severity of the rotor rubbing when putting down high power. For anyone else reading this and frustrated by the same problem, or to those who are simply curious, here are the results:
brake pads:
I tried 2 sets of brake pads I had in my toolbox. one of them is a bit taller (I think built for mtb), while the other one is a little shorter, but wider at the base (came stock with the cx bike). both are shimano pads. The hypothesis here was that a taller pad has a higher likelihood for the edge of a rotor to making contact. based on my test, this held true. the shorter pad was noticeably quieter during hard sprinting.
rotors:
This was most surprising to me. It made no sense that the shape of the rotor could impact how much it rubs against the brake pads, but in this case, it made a huge difference. the 2 rotors I tested were avid HS1 and a cheapo floating rotor I found on ebay (see below). The cheapo rotor was MUCH louder than the HS1 rotors, regardless of which set of wheels they were on. The two rotors are both 160 mm at the widest parts, and both measure 1.7 mm. I can't rationalize why the cheapo rotor is noisy AF when I'm standing up, and the HS1's are a lot more silent. I did notice that the cheapo rotors were poorly machined and assembled, so while I may have had them perfectly true laterally, they might not have been true radially. Go figure..
wheel (or more specifically, the hub):
I tested 3 wheels: mercury gx (good wheels), giant px-2 (sh*t wheels), novatec (just finished building them today, decent hub). the mercury and novatec hubs performed similarly: noisy with the cheapo rotors, silent with the HS1 rotors. However, the giant wheels produced a lot of rotor/pad contact while standing, regardless of the pad/rotor combination that was used. I believe it has to do with the stiffness of the hub itself. These disc hubs tend to have 2 cartridge plugs on either side, protecting the hub bearings from dust. You can remove them by hand, and I believe the excess play in these plugs are what causes the excess flex. All the wheels I tested had 0-200 miles on them btw, so the bearings are good.
so in conclusion:
- avoid sh*t wheels with sh*t hubs
- get road specific pads for road/cx calipers
- get name brand rotors