Position on my bike; opinions?

Some people like to size a frame initially by looking down at the front wheel axle when hands are on the hoods - if the axle is obscured by the bar then you’re in the right ball park. It’s not foolproof, a short or long stem can achieve this on almost any frame

If you’re comfortable then there’s no mistakes, there’s no correct fit for everyone. You would probably enjoy riding a smaller frame more because that’s why smaller frames exist - to put you in the correct position over the bike, but that’s something only you can decide once you’ve tried something else

It's difficlut to say without being able to see your feet, but to my eye your saddle looks a touch high.  YOu should be able to pedal powerfully in a circle instead of just driving down - with a leg. as stragight as yours looks, it's harder to pull your foot back at the bottom of the stroke

As a really rough rule of thumb, if you have your hands on the top of the bars, the front axle should be hidden from your sight by the bars.

The best way, though, is to go out with an allen key and change one variable at a time and see how it feels - saddle up, down, backwards and forwards until it feels good. 0.5cm at a time.

“I thought about smaller frame, shorter by 30mm, but in overall with 100mm stem it is only difference of 10mm in reach”

It’s not just the absolute reach measurement you have consider, that longer stem on a correctly sized frame will put you further over the front wheel and improve your weight balance

To me, you look too far forward on the saddle. You shouldn't be able to see any of the saddle protruding behind you.

What exactly do you want to know? The frame is too big by most people’s metrics, but you say it’s comfortable, that your set up fits you well and you feel the position is close to your MTB. So what’s the issue?

Looking at the photo, it looks reasonably well setup, arms arent reaching out too far for handlebars.  Maybe some core strenthening exercises. The plank, press ups, Romanian deadlift, front squats and some form of crunch will provide you with the strength

Comfort really starts with the layback of the saddle from the centre line of the BB as that fixes your knee position in relation to the cranks.

From there it is a question of what reach is comfortable for you, which will be governed by hip angle (saddle height), reach/stack and your flexibility/core strength. There is an optimum angle for this which depends on whether you're riding mostly in the drops or tops.

It takes time to adjust to a road position that's efficient. Usually if it's comfortable, it's efficient. Which bit of you aches the most after a 20-mile ride? Usually either knees, lower back, or shoulders will hurt first.

To me the position looks quite upright. What surprised me was that fitting a longer stem fixed my lower back issues, not a shorter one. It's counter-intuitive, you'd think a longer stem would put more pressure on your back but actually it means you carry more weight on your hands.

Whilst you can tune your position relatively cheaply with different stem lengths and angles there's only so much you can do with leg/knee position because seat post layback these days is pretty standard (either zero or 20mm)

Forget the position, I would worry about the weird rash thing on your face!

In all honesty, though, your position looks ok to me. How many hours can you do on the bike without discomfort? Can you ride tops, hoods and drops without feeling cramped or stretched? 

How do your knees feel during and after riding? IIRC pretty much everything about positioning stems from saddle height and layback, right?

Im 171cm (5”7) with a long upper body and arms. My road bike has a 52cm top tube and I have a 90mm stem with a 10mm spacer, since the head tube is very short. I do have the saddle quite far forward on the rails, too. Many would consider this all wrong, and I do get a wee bit of toe overlap on 172.5mm cranks, but it works for me. 

My point is that noone can really tell you if your position is definitively good or bad from a picture. Bike fitting is an art as much as it is a science. Yours seems to be ok, though.

Too small a frame by 2 sizes for my liking, I’m 6 foot and my frames are all around 555mm top tubes but I prefer my bikes on the smaller side. You’ve mitigated this to a degree with an 80mm stem but that’s very short for road riding, and a slammed -17 stem means you’re either flexible enough to go that low or the head tube is too tall - your picture suggests the latter. 

You can make it work to a degree with shorter stems, short reach bars etc but the geometry of the frame is putting your centre of gravity in the wrong place and that can’t be fixed. Maybe try asking club mates with smaller frames for a test spin and see how you go, or buy a ribble frameset in a smaller size

I’m a touch shorter than you. My best bike has a 543mm top tube and 11cm stem. So it sounds like our reaches are about the same, give or take a bit depending on spacers and stem angles. Handling may suffer a bit with a shorter stem. How wide are the bars? If the frame is big, then presumably your saddle is quite low so you’ll be more upright given the tall headtube. Position is quite upright, but not terribly so. Are you uncomfortable on the bike or just worried you’re not in the best position?

If you bought this bike from a "proper" bike store I would seriously go back and ask if they can assist. A good bike shop should offer good aftersales service.