I am currently using 6mm microbore made by Streamline because that's what the supplier had in stock last time I wanted hose.
Can't say I've noticed any difference between summer and this last cold spell.
Over the years I've used various companies microbore, it all has seemed to do the job.
For me, the problem isn't what is it like in cold weather, but how many times it can be pulled around garden walls etc, before it wears thin and leaks.
In my experience, all makes seem pretty much the same.