Here's a thought, for finding top speed without getting arrested, and with just a pencil and bathroom scale:
It's basically going to boil down to area, CD, and HP. Few of us have access to windtunnels, and some don't even have access to dyno's.
To get your HP, trap speeds in the quarter mile and weight have always proven to be reliable for me. They correspond very well to dyno numbers until you get quicker than 10.0, where aerodynamics kick in pretty hard. The less HP you have, the more accurate it is. ET's don't tell as much at trap speeds. You will need an accurate weight, and use any of the online drag calculators.
So mark off a 1/4mi. Start with a throttle stop of 1/4 turn. The faster the bike is, the less throttle you will set the stop at. You will only be using a fraction of your HP. Write down the your trap speed, plug it into the drag calculator to get your HP at 1/4 throttle. You aren't really trying to measure your performance, you are getting a number to use for the next step. Yeah, if you have access to a dyno, dyno it at 1/4 throttle.
Take the bike onto a flat road, tuck in, and see how fast it will go with the throttle stop. Using your HP number and a calculator like Willie posted, use a guess at your frontal area, and adjust the CD number until the HP matches your 1/4 throttle road speed. Now you have a good foundation of your total wind resistance.
You could do this without going past 75 mph if you set the throttle stop low enough, and it will give you a total drag number for your specific bike you could use for max speed calculations.
You could get the max HP by either 1/4 mi traps, or dyno, without the stop, then use the LSR calculator with your new area and CD. You will have to reduce HP for high DA if running at Bonneville or El Mirage.
You can use this method for also figuring out if aero changes work, if you don't change the engine output and keep the throttle stop around.
And nope, I have no idea how accurate it would be.
