What is in this scenario most natural / normal to do except of course to change the frame, when the saddle can not move further forward and I need to get 10-20 mm forward due to pain in the lower back after riding, I'm still fine in the arms / shoulders after riding!
hsea17

Unless you are putting out megawatts of power for your entire ride, probably a shorter stem. Unless this is some second hand bike that someone put a post on with a unusually large setback.

I just went from a 100 mm stem to a 70 mm stem on my Tarmac and I really like that I shortened it. But which ever you can find inexpensively to try will give you an answer of what to spend real money on.

One hint as to whether being able to move the saddle forward more is whether you slide forward too far when you pedal harder. Though that can also be other things, like too long a stem or saddle tilt. But if those things seem already within reason based on your elbow bend and what looks right for your saddle angle, then maybe your saddle should be moved forward.

Thanks for the reply. I had a "retul fit" once, set me on a previous bike at a seat height 74.4 cm and saddle nose to middle of handlebar at 49.3 cm. On the pictured bike below I end up with saddle nose to handlebar on 53cm saddle pushed all way forward. Saddle height at 73.5cm. Picture below but unfortunately not great for seeing the saddle setback.
hsea17

If the frames of the two bikes are different enough geometries and tube lengths, then simply transferring measurements to your contact points will leave you in less than optimal position.

Different seat tube angles, reach of the bars and stem added to the frame reach, length of cranks, fork rake and head tube angle all can make a fitted position on one feel right but so wrong on another.

When you move your seat you are changing your position over the BB and that not only affects how much weight you feel on the bars, but more so how you perceive the fit of the bike itself. And the least weight on the bars you can get is not always the best fit for power output. At least not for me.

IMO saddle position w/r to BB is more important than stem length. Here's my bike fit primer, go through the adjustments in order, see what happens: How can I fitting my bike

Below are the geometry on the two bikes in question however the dealer have offered to change the stem for free but because I don't feel uncomfortable in arms/shoulders when riding or after a ride I'm not sure if its that's the fit issue.

Geometry Details: Felt FR5 2019 (geometrygeeks.bike)

Geometry Details: Trek Emonda ALR 2016 (geometrygeeks.bike)

Compare: Felt FR5 2019: 54 -VS- Trek Emonda ALR 2016: 54 cm -VS- (geometrygeeks.bike)

Since bike fit is a combo of bike and physical geometry and centers of gravity, bike details are uninteresting. Just do the self-fit, see what happens. Even photos are uninteresting because one can't suss out muscular involvement or CG from looking at photos.

I ended up with a straight seat post which I had from before and got myself a centimeter or so more forward and so far that function well and the irritable niggling in lower back is gone (knock on wood) and the stem will be at the length it is for now.
Thanks for all the information.
hsea17