Geesh, @JPC , you're in Arizona, not Minnesota.
Your microclimate and mine are about the same, except our summers are ungodly and yours are unspeakable. But forget the summers for now, it's the so-called 'winters' we're about.
Which would not be called 'winters' at all in 95 per cent of the country. Forty-three degrees is a nice Memorial Day in Duluth.
Ray and Bob are absolutely right. Clothes make the man, or make him a Speedster driver, at least. The key is knowing what makes you cold in a Speedster, and it's not the cold, it's the wind. Start with a thin base layer, add some fleece, but most important is that wind-stopping shell.
Another thing to remember is that most of the wind in a Speedster is coming at you from behind. A good cap that covers the back of your neck is crucial. It needs to overlap your jacket collar in the back. Ever notice how all modern roadsters have some sort of wind deflector behind the driver? In a Speedster, you need a good hat.
If you're still cold, try an old-fashioned scarf tucked under your jacket collar. That can make a huge difference. And don't forget the gloves. A light pair of ski gloves with high-friction palms for gripping the wheel will buy you another five degrees or so.
The right clothes should keep you happy into the low forties, at least. Below that, who cares?
You're in Arizona.