Subwoofer help?

Hi i was wondering if anyone could help me....

i have a pioneer ts-w308 D4 12" sub runnin at 2 ohms.
My amp at 2 ohms only pushes out 265 wrms and at 1 ohm pushes out 500 wrms

i want to either change the sub to a ts-w308 D2(to run at 1 ohm) or add a 2nd ts-w308 D4(bringing both the subs to 2 ohms then bridging them to run at 1 ohm)

please advise me on which would be a better option and how much louder would it be to run 1 1ohm sub instead of two 2ohm subs..

TS-W308 D4/D2 (450wrms subs)

thnx alot excuse my english and my questions for i am a noob at this:confused:

would actually be louder to get two subs puttn them at one ohm. its twice the surface area than one sub. for the same amount of power, two twelves are gonna hit harder than one