I have a CCS, not the CCS2, so my experience may not help much. But I think that in terms of range, they are mechanically and electronically similar enough that useful comparisons may be made.
I have the old 48V 17.4 Ah battery, which comes out to a nominal 835 watt hours. I mention the watt hours because the CCS2 has a 52V battery. If we look at watt hours, the similarities are more clear. The 13 Ah battery provides 676 watt hours. Nominally. Good enough for discussion.
I've been able to get a little over 60 miles on a charge when my battery was new. This was on flat ground, very light breeze, averaging 16 mph, with weight around 300 lbs (rider plus gear), and using only the Eco setting. Rounding off, that's 14 watt hours per mile. If you used 14 wh/mi under the same conditions with the CCS2, then it would be right around 48 miles.
You couldn't get that range at 28 mph. These bikes are tuned to be more efficient at higher speeds, but air resistance chews up increasingly more watts the faster you go. Also, unless you are really fit, you're not going to sustain 28 mph in Eco mode. I've come close, in spurts, and I'm not particularly fit. If I want to go that fast, I put it in 3 or S so I'm not flailing away at the pedals.
When the company says you could get 50-75 miles per charge, they're not wrong. A 135 lb. rider on a flat, freshly paved surface, with no wind, using Eco, with no stops and starts, going 12 mph, could probably get 10-11 watt hours per mile, which would put her/him in the mid-60s range.
