lets think of it this way
Skill Level % ---- SP it would cost to increase
0%-100% -- 1 SP for 2% skill --- free 5% at these levels is equal to 2.5 SP
100%-130% -- 2 SP for 2% skill -- Free 5% at these levels is equal to 5 SP
130% - 150% -- 3 SP for 2% skill -- Free 5% at these levels is equal to 7.5 SP
150% - 175% -- 4 SP for 2% skill, free 5% at these levels is equal to 10 SP
175% - 200% -- 5 SP for 2% skill -- free 5% at these levels is worth 12.5 SP
+200% --- 6 SP for 2% skill -- free 5% at these levels is equal to 15 SP
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So, it would still be highly advantageous to get your tag skills up first, people would not wait till 24 to spend skill points, as maciek83 was thinking, in fact, it would encourage people to skill up lower skill early
right now, people just skill one skill till its where they want it, then go to the next, under this system, someone who wanted to get a bonus to sneak and small guns from the free 5% would want to skill them both early, tryin to get them up so they can get the best possible bonus from free skills