New Modem - Slower Download Speed?

I've been starting to have some issues with my Motorola SURFboard SB6141 so I went ahead and replaced it with a Motorola MB8600.

Running speed tests on the SURFboard were consistently in the 245 down / 23 up range.

Right before swapping out the modem it pulled 241.6 / 23.34.

However, a couple speed tests with the new modem are now pulling lower download numbers.  I've run three so far and the highest it's hit was 200.92 / 24.04 (other two were in the 170 range).

Why would a newer (and faster) modem be pulling lower download speeds than the old modem?