To the OP (from a roadie-turned-parttime-MTBer)
Get a drop-barred, geared road racing bike.
For a basic idea, put the measurements into this fit calc. It won’t give definaitve answers but will give you a rough range of top tube lengths to go for. Top tube is the important measurement for a road bike.
If you’ve never had a road bike, go and sit on some in a shop, don’t buy one online until you know more.
Don’t be surprised if you feel like you’re diving over the bars, you should be forward more than an MTB and you’re never going to need to hang off the back of the saddle.
Don’t be afraid to go up to 130mm for a stem, and ceratinly avoid less than 90mm – fast twitchy handling is not a plus on a road bike.
Get a compact double (50/34) chainset if you live in the flatlands – triples are for touring or climbing 25%ers at the end of 150 miles.
Crud Racer guards are now good enough to use one race-geometry bike in all weathers.