Buying & Selling the Wrecked Prison Bus (XP Bonus Question)

Didn't do heavy math, but I believe I netted at least 19 donuts at the last level up off of 24hr collider and 25 million or so worth of bloodmobiles. I've leveled up once since then too, which I doubt I would have without the left over XP from that run. I have a 450% multiplier and had all the SH buildings out since that's supposed to help.

Next level up I'll pay closer attention, but I'm pretty sure diminishing returns kicks in pretty hard after that.