Regarding the gearing combo discussion above- very few of us can crank out 80rpm on gravel using a 50/11 combo for extended periods of time, so the 'loss' of top end speed is more theoretical vs realized. It would certainly be lost if riding with the wind on flat or slight decline segments of road.
Point is, I dont think much is actually given up on that side of the gearing spectrum.
As for the original questions by the OP, there are endless ways to decide what bike to get since there are seemingly endless options. I would go with the below process to start narrowing down.
1- price point. eliminate bikes that are above your budget.
2- decide on drop bars or flat bars. eliminate bikes that are the style you dont want.
3- decide if you want to only buy from a shop or if online works(must understand how to interpret geometry charts).
4- decide if you want a specific material or dont want a specific material. eliminate bikes that arent the material you want.
5- decide if you want a specific style of gravel bike as there are some that ride like rigid MTBs and others that ride like paved road race bikes. eliminate bikes that arent the style you want.
5a- part of this would be tire clearance. Some gravel bikes max out at 42mm while others are 45mm and some at 50mm. Given you ride wider right now, this may matter to you.
At this point, start looking for specifics like groupset, compare wheelsets, look at differences like water bottle mounts, gear mounting points, etc.
This is where actual test riding would be good too since gravel bikes can feel totally different from one another by brand, or even by size within the same model due to geometry differences.
The other way to do this is if you are going to buy local for sure- just go to shops and try what they have. The checklist above will then be naturally checked off as you ride and try.