Just get a windshield that is fairly easy to remove, one that only uses a few bolts, or dzus tabs to put on, then on the hot days you can take it off...because it does cause the cab to be warmer.
I don't think I really noticed any speed difference. I did notice that it intensifies the rubber smell that comes from your CVT. It took me a while to realize it was the normal hot CVT smell and not me smoking my belt. You tend to hear all the noises you machine makes a lot more too. I need to address my front drive shaft, now it drives me nuts!