What Bryan V said. Listen to everyone's advice, but then decide whats best for You, Your sites, and Your hunting style.
fwiw, I have the 5x10 but rarely use it. I prefer the stock- I just slow down and concentrate harder when the going gets tough. I've had 6"ers on other machines and hated them. But again, that's me and my hunting style, sites, and preferences. (I have worked a site with each coil following the other on similar ground and found essentially the same amount of targets that I missed in both cases. But that may just be me.....but for me, that makes it an obvious answer). And all this assumes you are taking full advantage of the CTX Trace feature.