The 20" height calls for Zoomed 48" T5HO 10% with few plants under it to diffuse light and UVB. T5HO 5% is fine to use as well if the turtle can get a supervised 20 minute soak/bath 2-3 times a week in the outdoor morning sun. T8 tubes are pretty much useless at 20" height.
I agree. If your UV fixture will be 20" above the enclosure, then the first one you linked would be fine, especially with the plants as mikeh mentions. The stock tank would indeed position the bulb up higher.
The 5% or 5.0 would be an alternative for an enclosure with a lower height.