I've finally decided on getting the infinity kappa perfects, but I'm not sure whether I should get the 5.1s or the 6.1s. I have a 2004 civic and both will fit in the stock locations, but will the 6.5 driver sound any better than the 5.25? I was just wondering if there were any differences before I decided.
regarding output, the 6.5" is a definite improvement over the 5.25" size. for one, the 6.5" will be more efficient and have better midbass response than smaller drivers (they play a little louder and lower with equal power, and this is a good thing).
also, 6.5" drivers often have bigger motors and suspensions, so they can take more power and still hold up well over time.
i have a 6.5" component set in one of my cars, and the 5.25" version of the same set in my other car. the 6.5" drivers go a bit lower in the bass and distort much less at high volumes. however, at lower levels the two systems sound very much alike.