OP wants to know how far forward he can put his saddle while all responses address the opposite question.
A set back seatpost installed backwards will get you well forward.
I haven't used a sprung saddle since 1972, so I can't comment on the range of adjustment. No saddle on the market seemed like it would put me as far as forward as I wanted to be with my stock seatpost, so I bought a zero offset seatpost which did the trick.
