FWIW, I commute my 27 (or 18) on either a fasti'ish road bike, with no rear rack or panniers, or a touring bike with a rack and panniers. The panniers if I didn't leave clothing at work and need to carry them in or want to bring in lunch, or when I do a round trip of 36 miles total and can carry stuff. The faster road bike is my gravel bike, has 32mm road tires and I only carry, wallet, phone, house keys. Not really much time saved on the lighter bike as that's very much dependent on how many traffic lights I hit (Brooklyn, NY). Your situation may be different if little traffic ad few lights, then a faster road bike may save a few minutes at best. One thing to keep in mind is don't make a commute a fast training ride. You're mind set is to run lights, push the pace, etc..... greater chance for an accident (route dependent) but generally is just hard to do after a long work day (in my experience).