lol, well def. go with the 15"s. I currently own 2 10"L7 and have had 2 10"L5's. L7 are better but not by so much a gap as a 10" to 15". So definentaly go with the 15" L5's.
Now that is a close one, both the 10"L7 and the 12"L5 have the same power range. I'd probably still go with the 12", one reason is you can say "i have 2 12" in the trunk" the difference would be less however SPL would be greater with the 12"L5 due to more surface area on the cone. It seems like to me you can spend some bucks, so if you can and you like kicker look into their new competitions series subs called the SOLOX now available in 10" and 12"'s.