4ohm or 8 ohm

Im in the middle of a cubo 15 build and have been thinking long and hard about the use that these will get on the ocassions I will actually use them.
I supply the PA for my daughters Gymnastic clubs in house competitions and shows and up till now have managed to get a good standard of audio from my two aging 150 watt two way 12" speakers that also have twin ceramic peizo's and twin bass ports but I do have to ride them just under the limit for the job which is why I am building the Cubos to spare them of taking care of the bass elements and letting them take it easy in their older age lol.
I am not into big rigs and tbh will prob not add anything more than the two cubo 15's and one amp to run them with an active crossover and my existing amp and 12" speakers.
would it be advisable for me to go for 4ohm 15" drivers as I will get the best out of a new amp running one cubo a side?

yes defo go 4ohm, if you where to add another cubo per side too 2 a side then 8ohm drivers would be better, or you could just bridge your amp and run both cabs in mono 2 x 8ohm drivers = 4ohm load on amp.....

Thanks Bee just needed to clarify that.

and to add i will be running 500watts a side so to allow for a little head room a 1200 watt amp should suffice?

600w a side at 4 ohms, should be more than fine for your use..... i try to go 1 3rd more than the driver to give plenty of head room, but this is really only for live stuff, and heavey bass content music....