Thanks for the various replies and apologies that I haven't replied sooner - work has been busy.
My specific problem that prompted the initial query was the amount of stuff I could give to the newly 5th level cohort I'm introducing into a game next week.
Going by the formula Altamont posted I get 7425,86gp whereas Kigmatzomat's table derived from the treasures/EL stats gives me 7500gp for a character that has completed 4 character levels.
So I take it that assuming a fund of 7500gp won't get me into trouble with my DM or bring the WotC IP vultures down on my head?
One further comment to Altamont:
The table of variances you posted in your post critiqueing the level^3*100 formula doesn't appear to match the later stuff you posted. If we take the end of level 4 then a character could either have 6400gp by the formula or 7500gp by the actual table. In which case the variance listed in your table should be 0.853 (ie 1 / 1.18) rather than 1.18. I presume the same holds for the other variance values you have listed.
Regards
Luke