I know Sachs are very well used by my friends especially in VAG cars and they seem to be pretty happy but I have zero information about them in Kappas. There are GTs in Germany with their kits? Or they are thinking to develop one for our cars?
With 405Nm I would stay stock, at least I know the kit works and it can hold 350Nm as stock specs of the engine, I think I put the most stress on our stock clutch (tuned, nitro, bigger turbo, etc with over 200 launches at the races) that's why it started to slip around 17 000 - 20 000km but only in 3rd gear during races when I was pushing maximum nitro and doing 620Nm.
Now with 400-450Nm without torques spikes and not so many races I preferred to return to the stock kit, is daily friendly and no more unknown aspects, if it lasts 25-45 000km I will be very happy.