Hey there

Talking practically I would not suggest you to prepare for boards in order to clear exams like kvpy. If you would see the question paper of kvpy then you will find that they ask for the whole syllabus far before your college takes the final test of 11th. Also the toughness of the question is good and if you'll prepare for only boards then you may not clear it. So prepare for JEE level and then you can be sure about kvpy.

Good luck