Great advice all around. The biggest thing you can do for yourself is to match your cabs. Pairing a 15 and a 410 is no way to run a railroad. It's maybe doable if you're using a crossover, but even then--I wouldn't.
I think it's legit to go either a pair of 410s or a pair of 15s. Decide based on cost, weight, volume and of course sound. If you play high volumes you might want to stick with 410s.
And speaking of high volume, you probably do want some more watts. 500w @ 4 Ohms minimum, I would think. Maybe even more.
What cabs are these, by the way? I have a GK 410. Mine's the MBX line. Got it used for cheap.