What speakser can I swap into my 2007 CTS?

I have done a lot of searching and I read in one thread FlyFlip420 said that the Infiniti Kappas were the best you could use without frying your stock amp... however in another thread later on he states that the JL speakers are the best...I dont know what to make of this...someone please shed some light!

And if anyone has done this...how does it sound?

If youve swapped in other speakers please let me know which and how they sound...

Also what about the rear sub? I read kicker and some image dynamics mabye? Which is working out the best in the "free air" setup. And what does the JL cleansweep do? I keep reading I need it but I dont know why.

Thanks in advance guys!