If you are taking drums seriously - planning to gig, record and so on - then I would recommend replacing each of the cymbals individually, gradually, for high-end cymbals. It may be costly, but most definately worth it in the end if that's your goal.
If you are just wanting to step up your set of cymbals instantly, I would recommend the likes of the Sabian XS20's over the ZHT's. Honestly, in my opinion the ZHT's sound worse than your B8's. A logical step up the ladder would be the XS20's, which aren't too dear. They're pretty impressive actually.
If you decide to upgrade individually, for example, get a new ride - give me a PM and I'll be happy to give you more specific advice
Hope that helps
I play the Zildjian ZXT's (not the ZHTs), but having played these for a few years wouldnt recommend any of the cheaper end of the Zildjian series. My crash currently has the mother of all cracks in it, didnt last as long as I would have thought.
I'm saving the pennies to replace them one by one, custom A's or K's soon hopefully.
Yeah id personally change one cymbal at a time and spend the money, you wont regret it, i use all AAXs and literally hit these things as hard as i can and havent cracked one yet and ive had them for more than a year. In the past ive used stagg and zildijan scimitar but ended up destroying them in no time. Plus ive found the slightly more expensive cymbal sounds better, both live and in the studio.