Im running AXS, 48/35, 10-33. Flats? we dont got no stinking flats here. Rolling terrain, short punchy sections (2-4 mile), 20-23 avg, Its kind of a guess, Most rides are 30-45 miles. Actual avg depends on the climbing. Figure 1.8K-3.5K on avg per ride. Avg moving speed ranges from 14.5-18mph. There's a killer short ride we do for climbing 26 miles, 2600', I'll avg 14.5 on that . my favorite ride is 37 miles with 3,200' (2 long and very steep sustained climbs, one called "the corkscrew") and I target 15.5. I get to the base of the 1st climb which is ~8 miles into the ride, avg 18 or so, Im 14.5 at the top of the pass. It seems no matter how fast you go on the flats, you lose all your time on the climbs.
. A lot depends on head/side winds. Nothing special but I'm happy with it.
Descending speed: I am comfortable up to 45mph, after that I chicken out and tap the brakes. I hate the unpredictable winds at the Bottom of pass's where the mountains open up and you get all kind of crazy shit going on. My 72 Y/o Neighbor I ride with hits 47-48 which is about terminal velocity.
Gravel Bike: AXS, 46/33, 10-33 for little more range on loose climbs. Avg there goes down to 14.-15.5 on most rides same distances as road.