Welcome in the forum, Joe.
Most performance success you'll have with the antenna design for proximity switches. I think the PSoC family members do not differ too much in their sensitivity. But the MBR3 might be the best.
I would suggest you to create a Support Case (top of this page -> Design Support) to get in contact with a Cypress engineer.
Thanks a lot for your help Bob!
I am currently evaluating a wire loop with 14cm (~5in) in diameter vs a PCB trace using the MBR3 evaluation kit, but am not yet too happy with the achievable range. Lets see if the support can point me into the right direction :)