Here's a handy calculator to figure out how much power it might take to move your bike (and you) up to various MPH Speeds.
It includes Coefficient of Drag, and Frontal area inputs, as well as weight.
Drag, and frontal area are primarily what is preventing us from "going fast" given a stated engine power, and also what determines (other than right hand behaviour) what our overall fuel efficiency will be. The faster we try to go, the more resistance - squared - we are presenting to the air layer in front of us. Change some of the input numbers around to see the differing levels of impact.
Calculate HP For Speed
This is also why Bonneville Salt Flats Land speed record guys have super-dooper wrap around fairings, teardrop shaped bodies, skinny tires, etc. - to reduce the drag and frontal area.
Our Street Bikes generally run about .75 to 1.00 in cD, dependent upon the efficiency of windscreens, fairings, etc. Measure your handle bar width, times the measurement from the ground to the top of your head while sitting normally on the bike. Get the Sq. footage of this as your "Frontal Area".
Weight input should be your bikes weight, plus YOU.
Have fun, and note that anything you could do to reduce these figures will reduce the cD and/or frontal area, thus the power required to move that resistant big solid slug through the air! All good things.
Try different weights, and see the impact. Try different "frontal area" factors, considering a windscreen, a fairing, or just "you" tucking in.
Note the major impact if you change the cD a little, or the frontal area. If you "tuck in" and get your head low down near the tank... huge difference.
Your big chest, wide shoulders, and not-very slippery clothes are a major drawback, sort of a sail in the wind. Tuck in, wear slippery leathers, a streamlined and slippery FF Helmet, and minimise the frontal resistance if you can.
Note the difference in power required to move your bike up to say, 55 MPH, then try 120 MPH. Huge difference, as the bike and you are becoming harder and harder and harder to slip through the air the faster you try to go!
Have Fun, and ride safe (and slippery)!
Bob
CAUTION: This note added 2 days later!!! - Note that we are speaking only of "Horsepower" here. At Speed Trials such as Bonneville Salt Flats, etc., all one cares about is achieving a maximum "top" speed, so acceleration, reliability, smoothness, loudness, etc., etc, are all tossed by the wayside. A bike such as this would have almost negligable low-end torque, and you would have a difficult time just moving off the line from a standing start. Many of these bike require a team of manual pushers, or a vehicle to push them off from a start position, as the torque band has been adjusted waaay up the band for high speed purposes only. You would put on huge carbs or throttle bodies, hog out the intake and exhaust ports, have huge intake valves, a very long duration, very high lift, very high overlap cam, straight, open exhausts, and extremely high gearing to set up a bike for this. The timing is taken after long, running (Vs Standing Start) attempts, recorded both ways to compensate for wind, etc. Almost NONE of these "mod's" would translate well to a street bike. If you've ever watched or read "World's Fastest Indian", the Burt Munro story, you'd know that a bike like this won't ride well on the street, or an average race track very well. For straight line top speed events only guys! Just wanted to state this to prevent anyone from ruining an otherwise good street machine by doing any of this. 
Re: How Fast Can I Go? 
) folks claim to have done at BSF. This is a race for maximum recorded running speed, not 'acceleration' as many mistakedly believe. They are confusing BSF with a dragstrip!
