I can do it in 3 using Rage + Speed.
Anyway i'll tell you about strafe-jumping:
The first thing you need to master is using the jump key without using any force, just tap it, it will give a higher jump than you would get if you had no points allocated to jump but at no mana cost.
Now, observe people using strafe-jumping for yourself, they don't move from side-to-side except for evasion of enemy fire. The trick lies in pressing forwards and strafe but moving your mouse so that the resultant movement remains in the same direction, then strafe+forward with the other direction and again adjust the mouse to maintain direction.
Once you've mastered it, you can build up momentum, turn round aim, whilst continuing the strafe-jumps, this is essential in evading enemies if you are a flag carrier.
Anyway its more difficult to explain in words than to learn by following example. Join NL or BFCarnage CTF servers and ask some of the (nicer) players to help you out.