Anybody here have opinions on this amp:?

http://www.ikesound.com/Prod_Details.asp?Prod_Id=1188

Also, if my sub is rated at say, 150-160w RMS, what would be the best rating for an amp to mate to this?

Yeah this is a nice amp even tho its very large for the power. Alpine has very good sounding amps and would recomend i for your application.

As far as the RMS is concerned, i believe the amp was rated at 120@ 4 ohm for the 5th channel for the sub. Is it reccommended to have the amp at or higher than rms for speaker, or lower than speaker? I want to do my homework before I buy. Thanks.

Dunno about the amp specs dude, but what i Can tell you is....it is a GOOD thing to over power your speakers rather than under powering them, believe it or not....but lesser power can blow the speakers much faster than having more go through them.
some of the guys talking over at www.streetsourcemag.com were talking about this, and they all agreed on putting about twice the amount of power a speaker can handle.
which means if your speakers are rated at 90Rms then you would want power from your amps to each somewhere in the range of 180Watts. not much more than double though, you dont wanna get too crazy with it.
Anybody else agree with me?

Yeah I always run my Kicker Comps a little hot. I run about 80 over RMS and Ive had them for 3 years and they are still poundin like new ones. I suggest this also just make sure your subs arent cliping if they are you run a risk of blowing them. Run them to their limit but dont exceed that or your going to toast them.