I ran my MSD locked out for years, 35* all the time no problem. My ignition was setup so I could spin it over then hit the ignition if I needed to, generally never was a problem.

It did help it run cleaner driving around for sure. I have sence changed and use a megasquirt to control coil on plug ignition. Under light load I have the timing as high as 45* and it runs even cleaner and had a noticeable drop in temps when just putting around at low speeds, any load at all and it drops the timing back down. It uses a map sensor for the load.