I've owned two Onyx Vibes - a very underrated ball in my opinion - and I just picked up a Frantic, so I believe I can offer some insight here.
You say that your Onyx is too early. I'm taking that to mean that it's not getting the length you're looking for. Is that correct? Now, what surface do you have on your Onyx? The box surface was very shiny, so if you have it at box and it's still not pushing, you may have to put the pin up on the Frantic and possibly even consider adding more shine to it. I say that because, for me, the Frantic and Onyx aren't drastically different in terms of length. My Frantic definitely gives me more push and better hold than my Onyx, but it's not drastic.
Now, another factor to keep in mind is backend. For me, the Frantic is later and more angular than the Onyx Vibe, though both backend quite hard. If you go pin up, usually that's going to equal a ton of backend as well. I'm not sure if that's what you're looking for either.
Here's one additional question: do you bowl in multiple centers and/or on multiple patterns, or do you really only need 1-2 balls? I ask because the Onyx takes to surace changes as well as any ball I've ever owned. If you ever bowl on tighter patterns, I'd suggest taking the surface of the Onyx down to a matte 1000 or 2000. Doing so will give you a great option for tighter patterns, and it will create more separation between it and the Frantic.
Like Charlest said, if you were looking for more separation, a Nail (Fire/Smoke) or a Cobalt Vibe may have been better options. Nevertheless, the Frantic is an excellent ball, and so is the Onyx. I would simply suggest changing the surface on your Onyx and putting your favorite drilling on the Frantic. If the Frantic ends up being earlier than you'd like, shine it up like a marble to promote more length. You'll end up getting the reaction you want in the end.
