On our medium-high grip tight indoor carpet track we run a little harder damper oil and HPI silver springs on our TRF418 and with the center screw in on the top plate to allow for less flex.

Others run a little softer damper oil and Yokomo springs (softer) and the center screw removed, compared to us.

Guess its about driving style, but to us the softer setup with more flex provides maybe an easier car to drive, but also a lazy car, that tends to "hang" in the carpet in med-high grip situations.

The "harder" setup, on our track, provides in our hands, a car that rotates faster.