True, the turns would matter.
We have a local greenway by a river here that has some little jukes and turns and bridges. The KOM's are all like 24 to 25mph for long several mile stretches. Most in the 250 to 260w range. Usually with a 5mph or so tailwind.
I was figuring it may be similar. Maybe not?
Like others said, if you get a meter for the bike then you'll know for sure. I own a Kickr Core and do the proper spindowns and stuff. I've had it read low and high a couple times. Usually though, it's within a whisker of my Quarq for the TT bike. The whisker likely being reading at the crank spider versus the rear.
People's budgets are different, so I hate to assume, but if you can afford a smart trainer.........an on-bike meter for outdoors is a no brainer. Ebay, sales, etc.... You'll enjoy it!