It's not about wing though. I have a setup with 3 wing (1 less than this one) and it's way way more stable. Maybe it's related to camber settings. Funny thing is, this setup is faster than mine, but it feels slower, maybe it's because I like to push and drive aggressively, and this is too unstable in rear imo...I don't know mate how you did it, i was recently going with my own setup which was not able to go below 1.59.9 anyhow, but if you did with yours (which i just tried) 1.56.7 then i must say you a hell of a smooth driver, because your setup is very very sensitive in the rear as there is no wing at all. However after 15min i am not yet able to go below 2.3 and in fact i am way slower with urs than i was able to go with mine...
[Edit] Actually when you switch to medium its not that bad