I've gone the opposite way in my Radical Tour MP, Velocity 17g mains @ 52lbs/Cyclone 18g crosses @48lbs. My preference is for a softer stringbed and so far I haven't really gelled with a full poly or poly mains set up, in particular I find it hard to feel the ball on the strings when I am volleying and I'm often left with the sensation of the ball just sliding off the strings into the net rather than it going where I was planning.
I have been pleasantly surprised with the spin I am able to generate, it is by no means mind blowing but I can hit nice high bouncing and dipping topspin groundies, knifing slice backhands, wicked slice and good kick serves with this setup. I wouldn't consider myself a big string breaker but I have been surprised with the durability as well, however I think this has a lot to do with the dense 18x20 string pattern and the soft flex of the racquet. The Cyclone notched the Velocity fairly quickly, but the strings have only started to stay out of place for the last 2 hours, I would guess that I have 15 hours of hitting on this setup so far, I do not play many sets, I mostly just rally with my hitting partner for 2-3 hours a session with heavy pressure less balls. The Velocity is almost sawn through now and for the last 2 sessions I was sure I was going to snap it but it is still hanging in there.
I'd be interested to hear how you go with the Cyclone main/Velocity cross setup, the Velocity won't notch the Cyclone but the Cyclone will tear up the softer cross and it will be interesting to see how that affects playability.