If you do look at Miyatas (which are wonderful bikes...used to own a 710 myself and would welcome a old Miyata back in my stable at any point!), be aware that some of the higher end models that had internal cable routing through the top tube have had a history of cracking. I don't know how sporadic or common it is, but something to be mindful of.
Lots of great bikes and brands. Hard to give names, because I'd be leaving too many out! I can't remember who gave the advice (and at this point, I've probably heard it from many. Maybe it started with Randy Jawa?), but when trying to gauge the quality of bike from a picture, there can be a few good signs to look for -
-lack of 'turkey lever' brakes (the brakes with the extra lever for gripping in the upper grip position on road style bars)
-downtube shifters (vs shifters on the stem neck)
- lack of a huge shiny chrome 'dork disc' around the back freewheel (although, admittedly, my Fuji S-10S has one and it is an awesome bike and ride)
-forged dropouts
-aluminum cranks vs steel cottered
These are all indicative of a higher end bike, the more of these features the better, generally speaking.
Typically, the lighter, the higher end. It's a lot easier to make a 30lb bike than it is a 22lb, in 1970s and 1980s terms.
Sometimes, though, enjoyment will leave you baffled. I had a Zebrakenko (odd Japanese brand) and it was a higher end model. The bike was either around 23lb or sub-23lb...lightweight, higher end Suntour components, Ishiwata tubing, and I donated it in at the local co-op. Was very 'squirrely' to ride. In contrast, I've got the Fuji S-10S, with 27" wheels, 'hi-ten' frame, dork disk, and it weighs at least 26lbs...and the bike is a total joy...rides like a cadillac, tracks perfectly, super smooth, etc. Now, its not a quick ride per se, and I know that is your goal here, but the main point is that getting on a bike and riding it (assuming it checks out, safety-wise) is going to give you the best feedback. The bikes will start talking to you. Try to find a local bike shop that has a good selection of higher end older road bikes, and find some in your size and start test riding them. Or go to each LBS in your area and see if they even just have 1 in your size. Ride as many as you can. Start figuring out what you like and what you don't before spending a lot of money....
...is what I would tell myself if I was smart. Instead I buy up any old neglected project to bring home to the orphanage
