Interesting question and you can spend a lot of time doing research - but that is a big part of the fun in buying a new bike. I moved from a flat bar hybrid to a Spesh Roubaix, which is a great bike. I rode LEJOG on it and it performed well. Later on I bought a Titanium frame and built up the bike with handbuilt wheels and Ultegra 6800. It is super smooth and great for endurance rides and light touring as it will take a rear rack for panniers.
I sold the Roubaix and bought a Cervelo, which has a more 'racy' geometry, but is equally as comfortable as the Roubaix. I did a 94 mile sportive on it and didn't feel any more fatigued than normal. The other day I test rode a Storck Aerfast, which is an aero bike and different again from my bikes. Although it was only a short 8 mile ride I was surprised at how comfortable it was to ride. I was expecting something stiffer and less compliant.
I very rarely use the drops as I have back problems, but when I do I agree with
@PpPete that different bars can make a difference. I will have to change the bars on the Ti bike as I don't like them as much as the ones on the Cervelo.
Also Ultegra v 105. If you can afford it got for Ultegra as
@ianrauk says it is just that bit crisper than 105.
After all the bunny above enjoy the process of looking and trying. One thing is for certain - once you have bought the bike you will eventually look to upgrade! Probably the wheels first - then another bike - then more wheels then.........