A quick look at the link will show the available sizes for the seatpost.

To the OP: the indicated size of the seatpost gives two dimensions - the first one (27.2 mm) is the seatpost diameter, and the second (300 mm) is the length of the post from the bottom to the rails.

If your current seatpost's "minimum insertion" line is substantially below the seat tube collar then I would guess the 270 mm length would not be a problem. Going longer than 300 mm is better, albeit with weight penalty if you're a WW.