I like to get the best hardware i can afford. Upgrading Always costs more than buying it as a package( except in the most extreme cases (bikes in the $10-$15 K range.))

Sora is good stuff .... 105 might be a little smoother. But in your case .... if I were you, I can't say what I might do. if you ever want to go on a cycling vacation which might involve some hills, suddenly extra gears might make a difference. or, if someday you hit a Really serious headwind .... hitting just the right ratio can make riding in a stiff wind a little more pleasant.

Otherwise, try a 1x11 setup. Buy a cheap single-speed for variety. if you have a solid budget and you don't need anything special .... buy a solid bike with Sora a and a cheap single-speed. Try to rent a recumbent trike---you never know.

Another thing you might try is riding a bunch of bikes. If any one really sings to you ....

Carbon frames Can be a supple as the springiest steel or stiffer than stiff .... the only two things they are are a little more fragile and a little lighter. But ... not really more fragile unless you crash at ridiculous speed or get hit by a car, which would put a hurting on any frame ... and not necessarily lighter than good aluminum, if it is cheap carbon.

Also .... and sorry to be negative ... but this "Find a shop and buy their bike" stuff is All wrong.

First off, from what i hear, unless you are buying a $15K bike, the shop makes a lot more money on accessories and service than sales.

Even so ... you can change shops at will, but once you bought that bike ... it depreciates by a third the instant you swipe your credit card.

A shop worth frequenting will work on your bike even if you bought it from the competition ... but if you buy a bike you kind of like as a favor to the shop, and always wish you had bought a different bike, no one really wins.

Ride two dozen bikes .... why not? See what you like.

I know if i could only keep one bike it would probably be a CF, lightweight, Ultegra-equipped sort-of-racy bike, even though I am slower than a dead snail. I would be really hard-pressed to choose between that and my 105/Ultegra equipped CF endurance frame, which weighs about the same and is a little more comfortable on long rides (both weigh about 22 pounds, ready to ride---- tons of tools, tubes, pump, food, two full water bottles, lights and phone/computer... around 16.5 naked.)

Too good for me? For Sure! I will never stress either of them near their maximum performance limits. And I do dearly enjoy riding my other bikes, two which are 35 years old, and one which cost around $500 (though I have done considerable upgrade.) But if I had to choose ... why not a bike which is so light it feels like something is wrong when I pick it up after lifting one of my metal bikes .... and which has faultless, lightweight components? Too good for what?

Does every person who buys a Porsche have to take it to track days?

One other thing .... no bike will make you faster---that's the motor. So you need to decide what you like and don't like about your Bridgestone, and what you would want to improve.

Me, i'd slap a modern drivetrain on there with brifters, and add that puppy to my stable. I saw a few pics online---sweet-looking. I might even stay with moustache bars and just move up to modern thumb-shifters. If the bike rides well, keep it around.

But looking at the Bridgestone ... what do you like about it and what don't you?Look for a bike which does the good stuff better without the bad stuff? i don't know.

If you want a bike which is comfortable to ride quickly the Defy/Contend line is excellent---I checked it out when I was shopping for endurance frames. Fuji's Sportif/ Grand Fondo line is also good---both (IMO) offer good value for a good price.

But don't hesitate to treat yourself.

Never in my life have I Ever thought, "I wish this bike weren't so good." Not ever.