That’s with a P5 Three UCI legal or an NK1K with MAS cockpit. Firecrest 404 on the front & back covered w/ Wheelbuilder disk cover. Javelin helmet. 2XU aero sleeved skinsuit. NK1K is just a skosh faster than the P5 but not more than ~5W faster.
Yeah the 20mph is probably a bit higher, I was just looking at how I average 20mph during recovery intervals in the TT bike often with 175-180W avg, though that may be influenced by carrying in some speed from the interval. 250W is probably a bit low in realistic road conditions with regular road kits, but definitely doable if you had a newly paved flat with no turns or reasons to break aero.
Here you go, I don’t have a 40 km/h number as I don’t time trial / race. I am 1.80 and weigh 72kg (currently). The speed is 22 mph for imperial. Reasonably snug clothing but is not aero specific stuff.