We have two boxers and live in NE Ohio (I see you're an Ohioan too). They seem to keep warm on our walks but it's their feet that have difficulty. Just be mindful of the feet - we check the feet when they limp. It's a battle b/c we walk in the road since it's plowed but then they get salt in the feet (very painful) so, even though the sidewalks are more challenging I would say stay off the roads due to salt.
ALSO: We have the fido fleece for both boxers, but I don't recommend the fido fleece for two reasons: the hair is so drawn to the fleece and they aren't made for the boxers' broad chests. My mom has a boxer and she has a great coat that has a criss cross strap underneath and, waterproof shell on the outside and warm white stuff next to the boxer's fur.
Hope this helps.