For flat ground, I like the
12-25 in 11-speed. It
adds the 18 cog and drops the 11 cog. The 17-18-19 cogs are right in the 20 to 22 mph range, where I need close shifts to keep my cadence in the mid-90s.
(I have hills and use a 11-28) I occasionally use the 50-11 on long downhills, just to keep the pedals turning so my legs don't get stiff. I used to have a 50-13 top gear, and just coasted at speeds over 33-34 mph. I didn't miss the 50-12 or 50-11. I just don't understand why all the bikes now come with an 11-28 11-speed.
Here's the Mike Sherman Gear Calculator setup
for 52-36 and 12-25. The popup message just tells you that you can save the settings by bookmark/favorite the page.
The 52 chainring in black , 36 in red:
Try different cassettes, like the typical 11-28, and even try 50-34 chainrings. All the charts update on the fly.
The 52-36 chainrings move all the shift points up about 4%, or a little less than half a typical rear shift. (One cog shift ranges from about 6% to about 14%, depending on the cogs.) So you can go about 1 mph faster in the small ring before you run out of cogs. The tradeoff is a little harder hill climbing, of course.
52-19 at 95 rpm: 20.3 mph.
50-19 at 95 rpm: 19.5 mph.