I do not have a Quadra, I have a Performa, which is a lot cheaper.
And then you have all the LC Mac line, which many of them have a 68040.
But anyway, mate, go ahead, make a hardware comparison between a $100 Quadra an a similarly specced Amiga and you will find a big difference in price and availability.
On the other hand, running Aros on a 68k Mac is as usefull as running MagiCMac on it