Checking in from Minnesota. I have used or am using both sets of tires. While I haven't had any warm up or cold weather issues with the Contis I am currently running, I have to give a slight nod to the BT 021's in this department. The 021's grip seemed to be 'instant on' from the moment I first rolled down the driveway for the first time and was consistently great until I removed them and installed the Conti Road Attacks. My only complaint about the 021's was the relatively short life span: I flat spotted the center by ~7-8K miles. I only have ~4-5K miles on the Contis, but I am projecting them to be a ~10K mile tire.
As stated earlier, both will be a significant improvement over stock (D220) in terms of warm up and cold weather grip. They do have much different profiles and turn in characteristics: the RA is a taller, triangular profile (sharper, quicker turn in) while the 021 is a rounder profile (stable, controllable turn in).
HTH. Any other questions about comparing the two, let 'em rip.
[Edit: Couple other advantages for the 021 over the RA: The RA's slip noticeably for me on painted surfaces, particularly in the rain. They also slip noticeably over tar snakes above 85* F. No such occurrences with the 021's or other comparable modern ST tires I've used. I also don't hold the shorter lifespan of the BT 021 against it due to its lower price: the miles per dollar come out even against longer lasting, more expensive rubber.]
