Exactly. If you aren't planning to buy some upgrades soon, then go with the 13/18. If you are going to do some mods, let us know what you have in mind and we can better match an impeller.
Go for the 4" front air...and find an untouched 14/19 in the lists.
You will be pleasantly surprised.
You're gonna ask me why...right?...check the goodie list on a stage 1 kit. The only speed producing parts on the kit are the weekazz riva 3" front air and...that's right...a 14/19.
So...you can have an improvement over the riva air for way less than it's cost and a taller prop....safely.