I'd hate to have to choke down a roast that was cooked to 250F - I think it would be overly well done, perhaps burnt. I prefer my roasts to be done to a nice medium-rare, about 135-140F. My chicken about 170F. If it gets to 190F, I find it's way to dry for me.
My oven is certainly going to be 250F (except for that medium-rare roast - I love slow cooking.) It will even be as high as 500F for some things, but I make every effort to avoid touching the oven. And I would avoid having to heat chemicals that hot too.
Not keep in mind that professionally, I've cooked stuff to well over that for doing certain chemical analyses. One in particular was when I used to do fuel testing. I had to do distillation ranges on gasoline and diesel. to do that, you put some in a boiling flask, attach a thermometer and a condenser, and distill 100 mls of fuel over into a graduated cylinder. You recorded the temp for the first drop over, the first 10%, the 50% volume, the last 10%, and the last drop over. I seem to remember that diesels would go up to about 600F for that last drop. Pretty damn hot.
But all that was done using lab equipment, in a fume hood, and with experience doing lab work. I do not recommend the home darkroom people really play with doing stuff like this at home. At least not without proper equipment.