According to this document
http://stud3.tuwien.ac.at/~e0125557/sro/spgain.html by level 70 you will have the following SP based on your mastery gap: (0 GAP 73823); (1 GAP 90228); (2 GAP 110734); (3 GAP 137097); (4 GAP 172234)
BUILD OPTIONS AND SP REQUIRED
LEVEL 70 OPTION A [70 Fire/70 Lightning/70 Heuksal]
70 Lightning Mastery (MAX all skills except Light Imbue)
70 Heuksal Mastery (MAX Soul, Ghost, and Passive)
70 Fire Mastery (MAX Imbue and Nuke)
TOTAL: 177,544 SP Required (
4 GAP NEEDED)
LEVEL 70 OPTION B [70 Fire/70 Lightning/20 Heuksal]
70 Lightning Mastery (MAX all skills *except Light Imbue, Concentration, and Passive)
20 Heuksal Mastery (No Skills Taken)
70 Fire Mastery (MAX Imbue and Nuke)
TOTAL: 123,996 20 (
3 GAP NEEDED)
LEVEL 70 OPTION C [70 Lightning/20 Heuksal]
20 Heuksal Mastery (No Skills Taken)
70 Lightning Mastery (Light Imbue & All Skills Max Except Passive and Concentration)
TOTAL: 73,819 (
NO GAP NEEDED)
CONCLUSION: Option A has the works, but requires you to have a permanent 4 GAP, Option B seems a little more doable with a 3 GAP, and Option C looks fantastic with 0 Gap but at level 70, you will be wanting to unlearn Light Imbue and start putting points into Fire Imbue and Fire Nuke. But think of the fact that you leveled rapidly and efficiently without any Gaps and have most of Lightning Max.
Questions:
1. Which option would you all choose? How would you change it to make it better?
2. Is there a big difference in leveling speed between a 4 and a 3 GAP?
3. Is Option C a possibility even if you want to go Fire/Lightning at high levels, unlearn light imbue, and start focusing on fire imbue/fire nuke?