I use this exact combo a lot all the way through to really cold weather id adding a baselayer underneath. Brevet insulated gilet is the best piece of bike clothing I've bought.
My only complaint with the long sleeve core jersey is that in the size i take the arms are much tighter and it's hard to get an LS base layer underneath, especially merino
Would this be a good cold/autumn weather combination - longsleeve core jersey + insulated brevet gilet? I already have a longsleeve base layer.