When to draw the line..Remove all the trojans/spyware/bugs

or wipe, reload and reinstall everything.

I am running into systems all the time so infected with rogue antivirus programs, trojans, viruses, mal/spyware out the yang.

I first make a concerted effort to remove the infections, but there has to come a stopping point where you just have to say “That is enough” run DBAN to completely wipe, reinstall OS, ,etc… etc…

What are your guidlines?
As well what is in your virus removal arsenal?

I use a combination of AVG, SuperAntiSpyware and Malware Bytes to get rid of the worst cases. (sometimes these even fail)I find myself reverting to Linux boot disks and UBD4Win to boot around the OS, but still have trouble in some instances getting all the bugs cleaned out.

Thanks.