Warwick 115, one or two of them?

[isteen]

I have gone from 10" to 15" because I like the sound of the 15".
I use a TC BH500 with a Warwick WCA 1x15" - but that cab is 300 watt in 8ohm.
I am thinking of getting another WCA 1x15" - and here is the question:

Will it make the sound much larger?
I mean 300 watt in 8ohm will not be much in a 500 watt amp (at 4ohm)
2x15" at 300 watt each at 4ohm (2x8ohm) should double the volume.

Again, I love the deep full warm sound of the 15", but two of them - will it get muddy?