Re: Upgrade or more of the same: ZXL to BIIIX
I think the BIIIx would be perfect because you've tried it and like it. It will certainly have more reserve power than a ZXL, so therefore more versatile. In terms of build - I don't think you can get much better than Winston.
Someone mentioned the Zenith. If you like the ZXL and the Winston, I'm guessing you like a full flex and relatively slower action. I tried a Zenith a couple of weeks ago and boy - compared to my Winston's (GVX's, BIIt's, WT's) - it was like a poker. I know others love it, but maybe those guys like a faster rod.
I had a 8'9" 5wt Circa and it's a nice rod - a very nice rod... almost Winston-like - but it won't give you the versatility you're after.