Although there are several good filler materials, ER80S-D2, is one you should consider. This filler material is capable of producing welds that approximate the strength of 4130. ER-70S-2 is an acceptable alternative to ER80S-D2, as is ER70S-6, although the weld strength will be slightly lower.
Dont forget that 1" thick plate typically require the normal 300ºF to 400ºF pre-heat to obtain acceptable results. I would stay with 98/2 gas in spray transfer mode with .045-.062 wire for GMAW.