Wembley is definitely bigger.
As I said, most boxscores are in the 70k region with a more or less standard setup. Often even less:
57,292;
#BTS at Wembley Stadium; 06/02/2019
Taylor Swift: Wembley Stadium, London: 143,427 (100%) - $12,214,933 (2 shows)
Beyonce: Wembley Stadium, London: 142,500 (100%) - $15,301,688 (2 shows)
Billy Joel: Wembley Stadium, London: 57,804 (100%) - $6,575,093
Springsteen: Wembley Stadium, London: 153,904 (100%) - $25,259,232 (2 shows)
Maiden's setup blocks a lot of sightlines on the sides, so the capacity would probably be lower. 70k top, I would say