I planned to ride the 24. I have not committed with a registration but that is just around the corner. Today or tomorrow.
My goal is to ride 322 in 23 hours of pedaling. That will be 14 mph avg. To me it sounds slow but riding it will be different.
Will 140w take me that fast?
When I use
http://www.bikecalculator.com/ I get some insanely fast numbers. 140w = 19.3 mph I believe this is configured for a DF w/ aerobars. #190 rider + #30 bike
Ken, everyone is different and of course the weather conditions will dictate a lot as well.
My first "and only 24 hour" on my Vendetta (Sebring 2015), which I was totally unprepared for, I rode the first 12-hours at 135 watts and averaged 21.3mph. The last 12 hours I was off the bike for at least 100 minutes due to the cold and other factors (bad fueling, etc) so the last 12 hours I only averaged 16.8 mph. In the end I still ended up with 437 miles, which was well under my 500+ goal, but for a first attempt everyone thought I did fine.
Are you riding a Vendetta?
Whatever you are riding, if you can go out on a nice a flat as possible circuit and ride for an hour.
Set your Garmin so you can look at average watts for the ride (I put a special screen with Watts per lap and use that for a lot of my testing)
Just pay attention to your average wattage as you are riding for that hour and adjust as necessary for it to come out to 150 watts.
This will feel really slow and really easy - but as you mentioned, as the end of 24 hours it will feel "a little bit harder"!
Whatever you mileage is, that will be a good indication of what you can do (your bike, your body, etc) - mph at Sebring.
If you do not have a relatively flat place, then try and find a high school track or other and do the same thing. The speed will probably be about 1mph faster than you are going to be able to do on the open road, but it will still give you an idea.
Good Luck and let us know what you discover!