The OP wanted to hear actual personal experience with using RE050A or similar in cold/winter weather.
I have driven hundreds of thousands of miles using various high performance summer tires in mild (generally dry) winter weather and never had any problem. Temperatures were often below 40F but rarely below 20F and probably never below 10F. I generally never drive in snow on these but have driven in 1/2 inch of slushy snow in 32F for short distances without major problem.
My tires have included Michelin Pilot Sport, Pilot Sport PS2, Pilot Super Sport, Continental ContiSportContact, ContiSportContact 2, Bridgestone RE050A and RE-01R.
I would generally recommend great caution when driving summer tires in cold weather and would personally never do it on ice, generally not in temps below 20F.
However some of the previous statements have blurred the actual issue and differences between types of “high performance” summer tires. Some of the statements by Consumer Reports are misleading or flat out wrong.
E.g, they lump together all the recommendations using a single term, “Ultra High Performance Summer Tires”. In fact there are many levels and gradations – each with their own characteristics.
CR says these “Ultra High Performance Summer Tires” use a racing compound, are OK only for temperate areas or the race track, and have no practicality beyond that. This is an over exaggeration and gross oversimplification.
Among summer tires, there are ultra high performance, max performance, extreme performance and DOT racing tires. These are all different categories and have different characteristics. Michelin does advise not using or moving a vehicle having Pilot Super Sport Cup 2 tires in temps below 20F. Likewise TireRack says this about any “Track & Competition DOT Tires”. But those are very different from ultra high or max performance tires.
The GM bulletin mentions several tires including the regular Pilot Super Sport and says do not drive or even move the car below 20F. They lump all high, ultra high, max, extreme and DOT racing tires into the same category having exactly the same operational limitations re ambient temperature.
My guess is GM wanted a simplified bulletin making a blanket warning about any conceivable variation of a summer tire that might possibly have problems in cold weather.
Likewise the CR article says don’t use summer tires in cold temps at all, and in the same paragraph they state 40F. As worded, many will interpret that to mean anything below 40F is highly dangerous on any type of summer tire.
I have personally talked to Michelin and Continental representatives about this, and their advice was much less categorical. For ultra high and max performance summer tires they said they are generally OK down to 32F in dry conditions but as ambient and road temperatures fall, grip will degrade. I think most people know that, it’s just common sense.
There will be variation from one tire to another. I personally would be very cautious about driving in 30F temps with an extreme track-oriented performance tire like the Bridgestone RE-01R or RE-11. With a more general-purpose performance tire like the Pilot Sport 3, I would be less concerned about this but not cavalier.
For performance enthusiasts living in transition regions where there is seldom much ice/snow but winter temps can occasionally reach (20-30F) there is another possible option besides dedicated winter tires. There are ultra high performance all-season tires like the Michelin Sport A/S 3. I did not like the original A/S but supposedly the A/S 3 has been greatly improved.
Concerning specifically the RE50A I’ve driven it back-to-back with other max performance summer tires on the same car and I generally didn’t like it. It was quiet and smooth, but turn in, ultimate grip and predictability were less than top-rated summer tires. In general my impression was similar to how it’s ranked among similar tires on TireRack:
