Just my opinion based upon reading lots of accounts, it seems that lower volume and less fit DF riders will convert quicker to riding a bent than longtime roadies. Riders in flatter terrain will see equal speeds quicker than riders who live in steep up and down hilly terrain like in the Appalachians. A big factor is lung function acclimatization (and breathing training), in my case at least.
I have 15 months and around 13,000 miles on an 18-20 degree seat angle bent (not cruz) with 40,000+ miles on a DF in the prior 3 years of riding. It only took about 2 months and about 1,500 miles before the leg muscles were not sore from riding my bent but my speeds were terrible especially climbing. I had my legs but not the lungs and overall cardiovascular function. On the flats or rolling terrain, my bent speeds were about the same for a long time (maybe 8-9 months) with a very slight advantage to the bent on flat roads.
I am now breaking my former personal bests on certain types climbs but it took 14 months and doing a lot of innovative training to get there. On the flats, not chance for me to have ever ridden so fast on an upright. I have a 12% climb with an upright PB that is my target now. Just need the right W/Kg......or a new spine and a V20.
