I know you were asking specifically about G35's but:
MetalMatrix have been successful in other Infiniti's and are the standard Stillen performance pad on 4100 lbs Q45.
As with all performance pads, cold braking will be somewhat less but hot braking stronger (after the first half seconds of braking, all pads operate under hot braking conditions, but at 0F it may take an extreme performance pad a bit longer to grab, as it will grab at a higher temp).
The more extreme the performance pad the more pronounced this phenomenon.
The Metal Matrix are still very streetable and while their hot braking is improved their cold beaking doesnt seem to suffer too much.
As a matter of fact, I didnt notice any loss of winter performance with them