Being pointed by admin to this thread, all I can point to is that you've been running the FRS engine without a recirculating valve, standard or uprated, nor a basic twin piston dump valve. To get the chatter you did in those videos you posted, I'm assuming you've been nailing it around quite a bit with those key parts all blanked up. Wasn't a good idea seeing as how its a pretty tempremental engine anyway.
Basically, it runs temps of around 96C-101C before the fan kicks in, the first plug you killed (which really should have been Denso's and not crappy NGK's) was probably due to overheating
In other words, leave the DV where it is, if you want chatter out of a Focus RS then change the turbo with an external WG