Man,thats a hard one,and almost impossible to answer....The reason being,I don't think any egt's are calibrated the same,and the placement of the probe makes a difference too...I had an egt once that read 1225 at the highest I ever saw it...It was damaged by water and replaced...The new one useing the exact same probe,measured as high as 1450 a couple of times.....
All you can do is pressure test the engine,make sure it's jetted correctly with plug chops,and get a good base line setting.....Then you can use the egt as a reference....If it starts showing significantly different readings than your baseline,you know somethings wrong....
I personally don't use one any more because I have gotten to the point where I can tell from the sound of the engine wether it's running lean or not....After you get a good feel for the machine,you probably will too,and won't really look at the egt unless you feel like something isn't acting right.....
By the way,the cht reading of 250 is pretty good.....
Hoodlum