I am going to talk about SP gapping in this guide. I hope that it will be helpful for you, in deciding how much SP gap you should keep. Firstly, take a look at this table I made here. The table might be hard to understand at first. But read on and you will understand.
The SP gapping system in SRO is pretty simple. For example,if you maintain a 2 gap between your mastery and your current level (e.g. you keep your mastery at lvl 40, while your actual level is 42), you will earn only 80% the original exp and 120% the original sp. So if you killed a mob who was supposed to give you 1000 exp and exactly 1 sp, with 2 sp gap you will get 800 exp and 1.2sp. Currently SRO allows a maximum gap of 9.
Now take a look at column A, B and C of the table. Column A is numbered 1 to 9, where 9 is the maximum GAP allowed in SRO. Column B and C states the exp and sp, in percentage, that one will get at each gap. For example, at maximum 9 gap, one will get 10% the original exp and 190% the original sp.
Columns D,E and F is the cost-benefit analyst of each sp gap. Column D compares the exp lost when moving from the current gap to the next gap. For example, let's say you are currently at 2 gap, and considering going to 3 gap. As a result, you will go from 80% exp to 70% exp. The exp lost that you will suffer is (70-80)/80=-0.125=12.5% lost of exp. An more obvious example will be going from 8 gap to 9 gap, where you will suffer (10-20)/20=50.00% exp lost.
Column E compares the sp gain when moving from the current gap to the next gap. If you understand column D, this should be self-explanatory.
As you notice, the proportion of exp lost increases with a bigger gap, and the proportion of sp gain decreases. This leads us to column F, which calculates the ratio between the exp lost to the sp gained. For example, when you are going from 5 gap to 6 gap, you lost 20% exp and gains 6.67% sp. The cost benefit of this is 20/6.67=3 times. That means, you are sacrificing 3% of exp, in exchange for 1% of sp gain when going from 5 gap to 6 gap relatively.
Conclusion:
As you can see, the best choices are at 0 or 1 gap, since the trade-off ratio is one to one. Starting from the gap of 2, players will take increasing punishment as the gap increases. Until finally going from 8 gap to 9 gap, the players will be lossing 50% of exp in exchange for 5.56% of extra sp relatively. In other words for 9 gap, the players will be leveling twice as slowly, and getting only 5.56% more sp than 8 gap.
We can conclude that having giant sp gaps does not help. Increasing the gap cause one to lost more exp than the sp gain. So trying to zero gap, and then maxing gap later is the wrong approach. The best way for gapping is to keep a small constant gap throughout the whole character. The best is probably 3-4 gap all the way, since the ratio is still smaller than 2 before 4 gap.