I don't see why you would have any issues spooling 18g or even 20g TT's quickly. Ball bearing does not equate to faster spool directly. There are many factors involved. I don't have any issues with lag in my situation.
If you can find someone with a Greddy TT kit in your area, get them to take you for a ride. That will give you a general idea of how 18/18/20g twins will work out with GTM's application.
EDIT: for spelling errors
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2007 350Z NISMO #0618: Zerolift | UPREV | F.I. | Greddy | Competition Clutch | Injector Dynamics | Aeromotive | Pioneer | JL
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