This is largely out of date.
As it stands, it's a waste of gold to buy LS, for it's just 500k xp. SLS is 8 million now, not 80mil.
1bil / 8mil = 125 SLS from 149 → 150.
125 * 4 = 500 gold.
And if my math is right, this is total waste of ec:
125 * 120 = 15,000ec
.