OK:
I did some testing last night with a toaster oven in the garage.
Long story short, after two slices of toast and some fiddling around - the probes measured the same with 3ft of copper extension wire as they did without it.
I tested them by first doing a control, both probes hooked up as is, in the oven, at 350C.
Then I added 3ft of copper to one, and restarted the oven.
Then I added 3ft of thermocouple wire, and restarted the oven.
All results were the same + or - a needle width.
Hope it doesn't void my warranty
