Go to the swimming pool, have them in bikini, make the decision than.
Some girl might look like a 5-6.... but have 11 on 10 bodies
Some girl might look like 10 on 10... but have 5-6 on 10 bodies (cloth, makeup, panx) etc.
Personnally, at you age, I would go with what you can lay now and have fun.
Look aint everything... also at your age.... the 6 on 10 in High School might become a 10 on 10 at 25, the 10 on 10 at 17 might become a 6 on 10 at 25.... girl bodies change with time. Some are in their prime during High School, others during College, others at 30 etc.. and since you looking for sex... go for the easy option