Comparing the 46-cm Gran Fondo and the 50-cm Newest. Hard to believe both of these fit you properly. (Not Impossible---I generally ride a 56, but I have a 50 Dawes which is Really comfortable. I also have a foot of seatpost exposed, and a hugely long, up-angled stem, and a gigantic stack of spacers. My "right" frame size tends to be a 56.)

Here is another tool which helps some but not others: https://www.competitivecyclist.com/S...ulatorBike.jsp I like this one because I have an oddly proportioned body, and "standard" fit charts don't work for me at all.

Based on what i see here, you do not need a very expensive professional fit ... you need a very simple, very basic fit done by someone with no agenda and no desire to sell you a particular bike. A pro can adjust your body for maximum power and such ... but you need to figure out what riding position suits you best first. You shouldn't need to spend hundreds of dollars to get an accurate basic fitting.

if I met you and you were asking me these questions in person, the first things i would ask you would be, "How long can you ride your Newest comfortably? How far do you usually ride, and how long?" Then i would look at you on the Newest for a while and see how it seemed to fit you ... if your Newest has an adjustable stem i might play with that, or swap in a couple different stems, or play with seat height and setback and such .... unless you were already supremely comfortable on that bike.

if the Newest fits really well and you can ride for hours comfortable, then you want to pretty much duplicate the same spatial relationship of contact points---pedals, saddle, bars---on your new bike.

I cannot help much more without actually seeing you on the bike.

(The Gran Fondo is considered an "endurance-geometry" bike, designed for the rider to be sitting more upright than on a "racing" bike. The Newest looks to have more "racing" geometry. What attracts you to the Gran Fondo? is it what is in the bike shop and it looks nice? I know the basic design is good (because I ride the Sportif) but if you prefer a racier frame .... you might want to shop around.))