I've ridden when it's in the mid 20's a couple of times, I think it's impossible to be warm when it's that cold. I ride to school no matter what, it's only about 2 miles and I'm freezing when I get there.
i had to take the msf course again before i pcs'd...27 degrees that morning. it was me and the instructor and we finished in 2 hours! as long as it's dry i'll ride in any temp. the right gear goes along way...kinda like wearing a jacket if you are going to be riding a motorcycle...hint hint...
Mid 20's for 3-4 hr ride full leathers get stiff. I took the CRF70 around the neighborhood in a snow storm with 1' on the ground around 7 degrees with a 30-40 mph wind. But it was just a 10 minute rip so it dont count ,fun though.
I rode 45mins mid 20's to mid 30's for a couple weeks every day. No heated grips, just Joe rocket Meteor 6 jacket with line, KBC VR2 helmet, Ballistic 5.0 pants, Joe Rocket supermoto gloves with vented knuckles. I was shoving my hands in the radiator vents, and putting them under the rear to heat them back up anytime I slowed down. My hands were purple every day and would go numb for about another hour so I stopped riding and switched to the car. It usually doesn't get below the 30s but we get really cold streaks occasionally. The jacket was the warmest part for sure
I rode last week at 12F in Wisconsin (88) mile round trip to work. I just wore my snowmobile gear. Wasn't too bad. Get's a little nerve racking because the tires won't get to temp and are pretty slick. You really need to be carefull.