Hmm.. Tough question...
Ideally you would get a TI framed, disc braked Di shifting endurance/ gravel road bike.. which despite what others say is good enough to do it all
not of course that you want to limit your bike numbers...
Seriously tho.. I have a full on carbon roadie... a bespoke steel roadie and an Al/ carbon forked daily... The speed of each is proportional to the quality of the wheels on the bike. I have just changed my daily wheels (also now running 28 tyres versus 23s on the roadies) and the speed is now broadly comparable across the range;- they are all now in the Shimano Ultegra quality level.
I have test ridden this range:
renegadeseries and they are fantastic.... the Elite was amazing and I would love one.
At our age (hmmm) the rider weight/ fitness etc is a far more important factor than the bike itself... I know my 1986 bespoke steel frame is far faster than I can now ride it. On the same course, similar weather etc my speed, power etc are so similar on all three bikes that I must conclude that bike performance is not a significant contributor to the speed... my full race carbon is the least comfortable... my steel racer is the most comfortable and no slower. My daily is tough and fast.. not as comfortable as the steelie... not as nimble as the carbon... however with disc brakes it is, dry or wet the bike with the best braking ability and capability. which when navigating Central London traffic is a plus.
I'd easily commute on a ti framed, disc braked, Di shifting gravel/ endurance machine....
Second hand carbon is good, provided you are comfortable with not knowing its real history, one of the guys here did go that route and one snapped frame later was less than happy....