I really don’t see the 6 mph drop as a big deal … but winter tires are not necessarily advertised as high speed driving tires. They’re built for a purpose and I’d venture to say that anything above 55-60 mph, they aren’t going to be much different than a highly capable all-season tire. I believe tirerack only tests them stopping from a slow speed (20-30 mph) and again with a low speed acceleration test, and they do that for a reason. Winter tires are not high speed summer only tires, nor high performance all-season tires, they are designed for low speed improvements in stopping and acceleration in winter driving conditions.