OK, I'll be the first to weigh in...
Given what I know about both models, and what I can infer by your choice of instrument, were I in your shoes I'd keep the GK and offload the Mesa. Why? There's simply more consistency of tone between GK amps and GK cabs than is the case between GK amps and Mesa cabs - generally speaking. And because a Stingray played through a GK rig is a known winner.
Also
AFAIK, a class D micro head may not be the best choice to drive a Powerhouse 2x12 to its full potential - given the more robust Class A/B SS/hybrid heads and large tube heads those cabs seem to "prefer". Not to mention the slightly decreased efficiency of the Mesa Powerhouses, compared with the very efficient GK Neos.
But then surely you've already discovered these differences through your own playing, have you not?
MM