I'm also pretty sure that the 1935 FL Keys Hurricane was the strongest storm at landfall (presssure at landfall was measured at 892mb, I think, 4mb shy of the strongest storm at any time in the Atlantic).

That said, there is then only one storm that could've been more powerful at landfall, Hurricane Gilbert (888mb). Gilbert was near maximum intensity at landfall, but I doubt that it was actually at 888 (probably closer to 895 or something, which is still stronger than any Atlantic storm at any time except the two already mentioned. The other strongest storms in the Atlantic Basin are Allen (1980, 899mb), Camille (1969, 905mb) and Mitch (1969, 905), but these pressures were not at landfall.