The octane that works for you is going to depend on the condition of your engine, changes that have been made to the engine, where your timing is set, altitude where you drive, where you buy your gas and probably several other factors that I haven't mentioned.
Because of all the variables about all you can do is adjust (timing), experiment (with different grades & brands), listen (for pinging) and read (the plugs after a fast run) to determine what you need.
I use brand name regular (Shell) in the TR4 and it is fine. The TR3A doesn't seem to care what I put in it (somewhat tired engine though it doesn't feel like it).