Hi Chinoy,
I recently brought a RE Classic 500 in Hyderabad, India. For what its worth, I have not had any issues driving it at 100 kmph. My bike is completely stock, including the "Desi" tyres. However, I agree with what some of the others have pointed out, which is that you have to definitely break in the bike before taking it to 100. I experienced significant vibrations when I was trying to ride the bike at 100 before the 500km servicing. However, as the miles tag on the engine seems to be getting smoother and settling in. In fact, today, I took it out for a 150km trip and my odo read 813, when I hit the highway initially the vibrations still felt harsh at 100 therefore I went easy on the engine by pulling the throttle in and letting it catch its breath and then letting her have it again after 10 or so kms. After about 60 kms of doing this I could feel a noticeable difference in the performance. While coming back I was cruising at 100 without noticing and touched 110 with minimal vibration. I deliberately did not push the engine, but I feel that after another 500kms the 110-120 mark should not be an issue.
That said, it seems like you have a lot of experience riding, which I don't, therefore what you consider "smooth" running at that speed could be relative to my expectations. All I can say is that in my experience the engine performance has definitely obeyed the breaking in laws. My friendly suggestion is that dont expect her to handcuff you and ride you like a cowgirl on steroids yet, first court her gently and show her a good time.
Peace.