I think sabr uses a 15/20 on all of his 951s, best one he says. All carb model though. Probably will be close to that.....but I'm just guessing.
EDIT********See chart below....
From Mpros site:
GSX Ltd. 98-99 951 16/21 155.5mm SD-B6.0L SD-B6.0L, 6.5L SD-B6.5L
97 1/2 951 n/a 155.5mm SD-B5.0 SD-B5.0, 5.5 SD-B5.5
GSX RFI 99-00 800 12/25 140mm SD-A6.2L SD-A6.2L Call
GSX 96-97 800 17/24,16/23 140mm SD-A6.0, 6.1 SD-A6.0, 6.1 SD-A6.5
Looks like they recommend a 12/25 for a RFi