Alp,
In 2013 I went 143 mph with 45 hp. My spread sheet predicted I would need 52 hp to go 150 but I did it with 50 hp. It predicts that I will need 123 hp to go 200 mph with my current CdA. My spreadsheet is based on the principle that you need to cube your increase in hp to double your speed. It's pretty simple, really. If you want to increase your speed by 200/156 (your current record)=1.282, you will need the cube of this multiplier to attain 200 mph. So 1.28^3=2.1 times your current hp with your current CdA. Of course, with streamlining you should be able to cut your drag significantly. You be the judge.
Tom