With a 7 speed freewheel, a 11-28 will have pretty big gaps in the 15-20 mph range on the 50 chainring, and at 10-15 mph on the 34 chainring.

Speeds for an rpm range charts:

50-34 chainrings and 13-28 7 speed freewheel. The 50 chainring is black, 34 is red.



50-34 chainrings and 11-28 7 speed freewheel:



These charts are clipped from Mike Sherman's Gear Calculator. All the charts update on the fly if you change any of the settings.
Here's a link for 50-34 chainrings, 13-28 7-speed freewheel, 700c wheels with 25c tires. It'll pop up a notice that you can save this setup by bookmarking the page.

I did 80-97 rpm for the 11-28 chart so the highest speed on the chart is 35 mph, the same as the 13-28 chart. Otherwise the 11-28 shows 36 mph as the top speed, and resizes the chart, making it harder to compare.

The 13-28 is 13-15-17-19-21-24-28
The 11-28 is 11-13-15-18-21-24-28, so it has bigger jumps in the middle to add the extra 11 cog.

I'd much rather have the closer gears in the 14 mph to 22 mph range on the 50 chainring, instead of the faster top end of the 50-11.

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I have a Campagnolo 13-29 10 speed cassette for hills. On downhills, I'll effectively spin out at about 32-33 mph on the 50-13, instead of reaching 34-36 mph on a 50-12. I don't miss the 50-12.

My 34-29 is great on steeper hills. I can even sit down on 8% grades, at a slow speed, and use fairly light pedal pressure, no mashing needed.