It might give you a tad more power, not going to be much, might not be noticable. Because that's a pretty small amp. 10 guage should be enough, but bigger the better, go with 8 gauge to be safe. 4 gauge would be overkill and probably won't even fit the power connector on the amp.
4 gauge not only would be overkill but won't work as the amp isn't likely to be able to accept it, you could runn it through a slpitter but then you are essentially dropping a good chunk of change for something that is utterly useless. I would suggest sticcking with an 8 gauge. 10 gauge would work but with out knowing the specifics of what youare doing, I would say that you ought shy away for the sole instance that you are wanting a power wire that can provide an ample flow and a 10 gauge may not respond as well to power spikes as an 8 gauge would
Ok then I am assuming that you are bridging the amp, I did something similar with my setup and this is how I did it: I used 8 gauge power wire to the amp and then 10 gauge braided speaker wier to the sub. that provided all the neccessary interference contermeasures that i needed. I am thinking that this too ought to be suffice for what you are doing.