IMHO the smaller carb argument is just for best driveability and ease of tuning. If you want max power, then you'll still need the larger carb, regardless of altitude but I doubt your cam will pull in the extra air to need it, and big is certainly not needed for your intended use. And IIRC, at your altitudes, carbs are starting to go rich vs standard atmospheric settings, so a lean carb at sea level may be just about right up at you elevation.
And the carb size versus elevation situation goes both ways so I am not sure my thinking of going smaller is good advice. If you want the same power output, you gotta open the throttle to pull in more of that thinner air so a smaller carb will get into the secondaries, etc., sooner.