If you like your NRC's, I think you could look at the Ride Capos. They're about the same in terms of stiffness and response. If you want to step up in response and stiffness, the El Hefes would be a good option. Personally I'd put a set of Capos on a Heritage, but it's all personal preference.
Diodes are good, Rome Targas should be given a look too, I'll pass on Unions.