Well my question has more to do with when it is appropriate to adjust roll center and when is it appropriate to adjust camber gain. I would view roll center adjustment as having more to do with how much traction/friction there is (more traction = less need for weight on the outside tire "mid-corner" to generate grip = higher roll center), which is a combination of the track surface and the type of tire you're using, while camber gain has more to do with optimizing the tradeoff between forward and side bite for a given track layout. The problem here is that, when you change your roll center, you change how much the chassis rolls and therefore how far along the camber gain curve you end up traveling (camber gain itself also changes slightly, but let's ignore that). So basically, if I set my car up for a lower roll center, I may need more camber gain (shorter upper link) to keep the wheels from going too far positive at full "roll," while if I have a higher roll center, I may need less camber gain to keep the same contact patch at full roll. In other words, changing only the roll center without changing the camber gain can result in a misleading interpretation of where you're getting your "grip" from (i.e., weight transfer or contact patch).

Applying this to my T4, the reason my T4 got loose on me, I think now, had less to do with roll center and more to do with not enough camber gain for that particular roll center setting. I probably could have increased the camber gain and achieved the same cornering stability, albeit at some cost to forward bite (which could be addressed with more anti-squat).