I also have the 265/50/20 Toyo Proxes II tires. So far (in my limited ownership) I have been impressed.
They ride soooo much smoother than the OEM's. I spoke with the master Infiniti technician at Sewell Infiniti in Dallas, and he said that the OEM Goodyears had a ton of complaints. He said the OEMs were too soft, and would wear out within 15,000 to 20,000 miles, and that there have been a lot of unhappy customers.
He said that only the OEM Goodyears and these new Toyo ProxesII were the only 2 tires that Sewell was 'approved' to put on any new or used Infiniti FX models...
To the actual tire--
Keeping in mind that mine are brand new (I will also try to do updates as I accumulate more mileage), they handle excellent. I have never had any slippage, or and road noise is far superior over the OEM Goodyears. They ride very smooth, and have handled wet surfaces with ease.
Living in Dallas, TX... I obviously haven't tried them on snow. I appreciate the 'aggressive' look to the tires including the tread design as well as the low profile-esque look.
So far, I am very happy that I had the dealer put these on as part of the FX purchase negotiations...