Please try and stick to the stock size only. The 100/90 will have a higher profile (sidewall height) as compared to the previous 90/90 spec tyre. Going for a fatter front tyre with increased sidewall height will result in a heavier front-end feel than before whereas the 'turn-in' effort will be more. It will affect the handling/maneuverability of the bike adversely. Go for the stock MRF Zapper FS, it's a great all-round performer.