Sony XM-4045 vs. my HU CDE-HD137BT

[1996BLKBauer]

OK, so my new Head Unit Alpine CDE-HD137BT says 50x4, so I am uncertain if this is RMS power, or peak power? I am fairly certain it is peak power. and my amp I picked up with a deal a few weeks back says 40x4, once again is this peak, or RMS power? Which would be better to run my 4 door speakers, which are Alpine SPS-517's? I cannot understand how a HU could produce that much RMS power, I also could not imagine an amp, even an older one like mine to produce such low RMS power. SO if anybody knows anything about this let me know.

[1996BLKBauer]

So after some research, I found that the Sony XM-4045 has a RMS of 40watts @4 ohms, with 4 channels.It also has peak power rating of 90watts @4 with 4 channels.

I also found out that the Head Unit, the CDE-HD237BT has an RMS power of 15watts @4 ohms, with 4 channels. It has a peak power rating of 50watts @4 ohms, with 4 channels.

So I pretty much answered my own question, and I am going with the Sony amp, because its RMS power is 10 less then the peak power of the Head Unit. My speakers handle 75 watts RMS, and 230 watts peak. I am sort of kicking my self for not getting the Hertz speakers I heard, but they would have made me go $40 over my budget.