I think Martyn has explained it pretty good above.
The Kick Angle (aka the rake) helps to resist weight transfer during cornering which I have found helps to smooth the corner transition out of the bend.
If you can't get hold of the 5 deg blocks currently, try the 3 degree ones - it's worth playing with and (IMO) the 25 degree kick angle does make the car feel smoother throughout the entire turn but, as RacingDwarf has pointed out, 25 + 10 deg can make the car feel a bit too unbalanced.
It seems that around 30deg caster in total is about right - I prefer 25 deg rake + 5 deg caster block as opposed to the 20 + 10. If / When I break my 5 deg blocks, I'll go to the 3 degree before I go back to 20 + 10.
@RacingDwarf - Dave - can you post your rear motor set up please? I hear its ace
