Many of us find "gear inches" and easy way to visualize gear ratios that the straight ratio fietsbob uses. It is also a language that has been around a ;long time. "Gear inches" (GI) is what a single wheel wopuld need to be to roll as far as one pedal stroke; in other words how far a high wheeler of 140 years ago would go (or a kid's tricycle). 70" is what a big high wheeler would be and also makes a nice all-around flat ground gear. Above 80" is starting to get big. 90s are full on race on the velodrome.

Your gear is 48 / 15 X 27" (roughly your tire diameter assuming common 700c) = 86.4", pretty big.

As for chainring size, bigger means bigger cogs also to achieve the same GI. Slightly heavier and very slightly more wind resistance but a little more efficient and long wearing. (An aside - running 1/8" chain, rings and cogs as opposed to 3/32" has many of the same advantages/disadvantages.) I run 1/8" and a 42 tooth chainring as I want to be able to go to good hill climb gears, am 65 yo and never had your kind of speed. In my racing days, the fix gear was primarily my poor weather/winter bike and after my first season of racing I rarely went higher that 42-15 at my strongest mid-season.)

Ben