mughals converted majority of the high caste bengali hindus to islam
even majority of the punjabi high caste hindus converted to islam
Mughals or the Afghans before them and the Turks before them who fought their way to India and immigrated to this land were warriors. They were not preachers. So, Mughals did not convert any one, at least superficially, but the Faqirs, Darveshes, Mullahs, Shaikhs, Khwajas and Syeds whose main passion was to spread Islam, had converted both high and low caste Hindus to Islam. Anyway, Islam does not accept a caste system, therefore, we do not have to care whether some were low or high. All are equal human beings.
It happened during all the dynasties, but, in case of Bengal, it seems that many local Hindus converted to Islam during the Mughal period. Emperor Akber sent about a 1000 pious Muslims to Bengal after it was occupied by his army. I agree with the statement by Captain_Planet that we all have become mixed blooded people with strains from different races as Islam encourages marriage among the races. Same thing happened to all the Muslims of the sub-Continent during their 800 years of stay.