Lots of variables with wind, body position, etc.

I still think it's pretty close. I spend a lot of time at that speed taking 4-7 minute pulls during group rides (same roads, similar wind, etc.), so I think I have a good feel for it.

Any yes, I do feel it is significant at speed and I don't regret spending the money on aero wheels. Like I said, "nice, but not huge". I'd still much rather add another 15 watts to my FTP vs. bolting on a few watts via wheels. That said, I'd take both if I can.