I'm afraid that such lovely days as today - especially as winter is approaching - are probably the most dangerous to fly on.
So many GA warriors and training flights leap airborne to take advantage of the weather that congestion is inevitable and the 'Big Sky' theory of avoidance just doesn't work.
As someone has already mentioned, visibility from high-wing FW is poor, especially above or into turns - I have been nearly taken out several times as one has climbed through my level without seeing me.
Transponders and TCAS should be made compulsory for all GA.
My condolences to the bereaved and their families and friends - another sad day in aviation.