Ok, pulling out calculator:
Expentntial Reg:
money = 31674*1.1^level
87th level = 126,000,000 gp roughly
Power reg:
money = 141* level^2.4
87th level = 6,400,000 gp roughly
I don't think it's exponential. True the exponential regression comes closer, but I only have 10 points of reference...