If all you are running is the radio, and the stock power cable will reach, it will work fine as is.
There are a few reasons why you would need to go to a larger gauge cable:
1. The distance to the power source.
2. Increase in current draw.
The longer the wire is, the more voltage drop there will be. This shouldn't be an issue for this radio if you are using the stock power cable. Upgrading to a larger gauge isn't going to fix anything. While it may reduce the amount of voltage drop that the stock power cable has, the result of upgrading isn't going to amount to anything noticeable.
If you are only running that radio, then needing additional capacity isn't required.
Where you might want to increase the cable size is if you are planning on adding additional radios in the foreseeable future. Running wiring can be a time consuming task, so if you think you might want to add more radios down the road, put in a larger power feed now.
I ran a 6 gauge power feed in my truck to a point behind the rear seat. I have a distribution block there where the power is fed to two different radios. It was much easier to run one larger cable than two smaller ones.
Using the stock cable is fine. Just make sure you make good connections. Make sure the wiring is well protected agains sharp edges, heat and other damage.