Warp scale was never linear. TOS scale was something along the lines of v = f^3 * c . So Warp 1 was lightspeed, Warp 2 was four times the speed of light, Warp 3 was nine times... then they shifted it for TNG with Warp 10 being the maximum speed.
Thanks, I thought I'd managed to get my computing degree's algorithmic complexity shit out of my head for the evening.
Wine factor 9, helm.