Hi Tibono,
We are talking about pondering.. Computer B gets full 30 seconds to ponder = 3000 not 1000. Only computer A gets 1000 at normal speed. Computer B has 3x speed = 3000. I am talking about time each computer gets to think while pondering only and not while calculating a next move.

4x speed factor
1) Computer B moves in 7.5 Seconds = 250 Positions Ponder for Computer A
2) Computer A moves in 30 Seconds = 4000 Positions Ponder for Computer B (4:1 Speed)
Pondering = 16:1
Non Pondering = 4:1

So you can really do:

2x2=4 Pondering handicap at 2x speed increase
3x3=9 at 3x
4x4=16 at 4x
5x5=25 at 5x

So if you increase to 5x you have 5000 moves divide by 25 and you know up front how many positions the 1x computer gets under ponder. In this case 5000/25 = 200 positions.