You're all very missinformed sub size doesn't make SQ or anything like that it has the same parameters just different cone size there is no audible difference. The size woofers you get depend on the freq ranges you want, the type of vehicle and if you want SQ/SPL or SQL.

Answer these questions and I can help:

Do you want Lows or Highs or in between?
Can you obtain or build a custom enclosure?
What music do you mainly listen to?
Will you compete or will this be daily/music?
What type of vehicle do you drive?

Your car should handle the 2500w output from the kicker @ 2ohm so long as you play it in short period until electrical is built up. I have a friend running a ZX2500.1 in his car off just 2 stock batts and a stock alt and it does fine. Stay away from kicker speakers though I would recommend: Obsidian Audio, Sundown Audio, SKAR Audio for budget woofers. If you have an SUV grab up 2 Obsidian Audio 18's tuned around 33hz in a 10ft^3 box should hit lows/highs and yield some nice SQL that's just my take though.