At 25mph on the 53t & 11t gears, I'd pedal about 65 rpm. Here are the numbers (in mph) I got for my setup at 80 rpm of the crank off off Sheldon Brown's gear calculator http://www.sheldonbrown.com/gears/:

53t 39t
11t 30.7 22.6
13t 26.0 19.1
15t 22.5 16.6
18t 18.8 13.8
21t 16.1 11.8
24t 14.1 10.3
28t 12.1 8.9

With electric bikes, you'll want higher gears because you generally ride faster. I used to have a 50t front crank but found that even with an 11t rear cog, it wasn't enough and found myself using the last two gears too much, wearing them out much faster. Now with the 53t, I use the last 3 gears when cruising and I have a lower cadence for the much higher speeds.

I've never ridden a PL350 so I can't compare, but I heard that the 350 has better hill climbing capability. I think the PL500HS low speed torque is probably slightly better than the 250 or about the same.

I did the no load speed test once. It was about 41 mph.

The freewheel was hard to find. Harris Cyclery used to have these Shimano 7sp 11-28t FW, but they were out of stock for a while. Then one day, I asked the REI bike shop and they happen to have it! It's not a stocked item, but it was in their repair shop. So I bought two of them.