Higher skills equal higher salaries.
http://www.google.com/imgres?hl=en&safe=active&sa... I kid, I kid :D
1) It depends which skill is phenomenal and which one is marvelous. For example, 18 HA isn't worth the salary that 15 HA is because there is little increase in better handles, and the salary unnecessarily spikes.
2) Feel free to correct me if I'm wrong, but I think for an SG, the skills that can cause the highest salaries (assuming the skills are equal) are JS/JR/OD, then HA/DR/PA. For PG, I think it is OD/HA/PA, then JS/JR/DR. For SFs, JS/REB cost more. For bigs, IS/ID/REB. Not sure which one would cost more.