I can confirm from my digging that two towers have B41 LTE, and I think the B26 is still being optimized. Pretty sure the sites are awaiting backhaul, too because I never go above 10 mbps on the B41, although back in December I hit 60 mbps.
North DC area is a lot better, was up there to visit family, hit B41 almost the entire time. Speedtested 58 mbps and in the 50 range very often for miles.