rythmik 250 or 350 for assassin

[donkey]

Hi there. I haven't posted on here before but I need a liitle bit of advice. I built boxes for two assassin 10's and am wondering if 250 watts will do or should i get the 350 just to make sure. Money is a bit of an object here but if it will make a difference then i will do it. The subs are in 40 liters net each sealed. Room is 12x17x8.
Also how useful might the extension filter be on the 350 in my situation. Has it been useful for anyone else?

I am ordering these with the 24db crossover to make sure no higher frequencies are present in the sub.

I have temporarily been using these assassin subs in thsi configuration with a cheap car amp off a 12 volt power supply and i am still impressed with the quality and crispness of the sound. Definitly a sleeper sub.

Thanks guys