Based on specific gravity, published values:
Gabon ebony specific gravity at 6% is about .86
Hard maple s.g. @ 6% is about .62
so GE is about 1.42 x as dense as HM at the same MC.
Based on published "dry weights"; 44 for HM & 60 for GE, the ratio would be 1.36
Relating to cues, Joey always seems to know what he's talking about, so if a solid hard maple butt @ 29" long weighs 13 oz; then the exact same dimension butt in GB ought to weigh 17.7 to 18.4 oz.
I've never made a solid ebony butt, but that seems about right, considering other wood that is close. I've made a few 30" butts and it can be difficult to get the weight out of them with dense lumber to start.
Diameter matters - whether you like the ever-more slender modern shapes in the 1.250 range, or prefer something around 1-5/16" or even thicker.
That said, I'm primarily a hobbyist maker & not very active at that..
smt