blackcom i cant say by comparison since i dont own and have never played an 800 but i have the 1U 1000 and i play loud metal. the 1000 and axe fx replaced 2 dual rectifier rackmounts. at 4ohms the 1000 has about the same overall power as a dual rec so each side replaced one of my duals. as far as tone its amazing and never in my life would i have thought that my holy grail recto rackmounts could ever be replaced, and DEFINITELY not from a 1U 8lb solid state power amp, but its happened and i couldnt be happier..