(I hope I got this right)

The SPD value is the speed’s relation to the current tempo. 32 is one full cycle in 64 steps, and so 16 is two cycles in 128 steps etc… The multiplier, then multiplies the speed (duh), so speed of 32 and multiplier of x2 means two cycles in 64 steps (1 in 32) and x4 four cycles in 64 steps (1 in 16).

Your example of 4 x2 (=8) would be one full cycle in 256 steps, as it’s four times slower than 32x1.

Oh and negative speed means running the LFO backwards!