With the current shock technology out there and Firm Feel's willingness to make a custom diameter t-bar, I'd say that the rates are pretty well covered for everyone but all out race efforts. By using custom splined s-bars with modular arms, they will yield better on road handling and ride improvements for a street going car than going to wrist sized t-bars.

If you still need something bigger than a 1.24 t-bar for your race car, you can always convert to C body sockets and talk to Firm Feel about custom t-bars they can tool up for you in the 1.40 range, which is upwards of around 750# wheel rate, or roughly twice what the Hotchkis Challenger is using currently.

The only big advantage I could see of using the splined adapter in a stock suspended mopar would be to give you less expensive bar options so you could carry around dozens of sets to change out for track conditions. Even at that, you are only saving 50% per set, but, you also have all the upfront costs for the adapters.