As a previous E39 M5 owner, I'll join in the "don't do it" chorus.
Fantastic car in it's own right, don't get me wrong. One could even make the argument that the higher displacement S62 made for a more relaxed daily driver - when it wasn't drinking a small refinery worth of crude oil a month. But handling is not in the same league as the E90/E92 and maintenance costs will make you cry. Adding forced induction to your current M3 is clearly the better path.
2013 Audi S6, Ibis White
2008 E90 M3, Jerez Black, Black Nappa, Brushed Aluminium, 6-speed, Premium, Tech, Cold Weather *sold*