I once rode a back-to-back comparison on my Birdy and my Swift on the commute. I was wearing heart rate monitor on both cases. For those 2 commutes, my heart rate was very close to the same for the two days, and unexpectedly, so was the average commute times. I expected the Birdy to be slower but it was just as fast.

I would have to do some digging to see if I gave the actual speeds on those cases, I expect it may have been around 27km/h ie 17mph. My best ever was 30km/h for the 27km commute. So based on that I would say yes, the Birdy, if wearing Kojaks, would be just about as fast as that, maybe a few % slower. My perception was it is slower and I found that perception counts a lot because I imagine I get more tired. I get the same effect when riding on slightly wet roads, it feels harder.