I always try to match or exceed the recommended RMS power for the subwoofers. For example if you have two 300w RMS subwoofers I would recommend an 600+ watt amplifier. Will a 500watt amplifer work? Yes...but a 600 or better yet 700 watt amplifier will work better.
Both of the amps specified are alright...for a single subwoofer. I know they are having a deal and everything but you only need one 12" in a car the size of a Protege5, especially since it is a hatch back and you won't loose any sound in the trunk. Plus it doesn't look like you have plans to power your front speakers with an external amp.
For amps and subs, I would recommend MTX over Infinity.