Actually, I think a .393 in RFK is more impressive than his .400 season in Coors, although .400 is obviously the magic number. The number of singles and HR's lost to RFK vs Coors would certainly put him well over .400(at least I think so).
599 131 242 53 2 41 133 91 105 4 1 2 .404 .484 .705 (Coors)
586 103 230 47 2 26 109 90 88 0 0 1 .393 .471 .613(RFK)