EGT gauges will read slightly differently for different cars EVEN WITH THE SAME 
MODEL AND BRAND OF EGT GAUGE.

If you want to make absolute sure what YOUR safe temps should be, get the car 
on a dyno with a wide-band.  This will verify what is safe and what is not.

The EGT gauge is one of the most misunderstood tuning tools, as interpreting 
it's output is not very straight-forward.  Wide-bands have always been popular, 
because you shoot for a target number, and reaction time is quicker (versus EGT).

EGT probe placement is also paramount in how the EGT gauge reacts and what kinda 
temps it displays.  Funky exhaust gas resonances can mess up readings off the 
EGT gauge!  I've tuned a big turbo FC running a divided turbine set-up that has a 
GReddy EGT installed with the probe in the downpipe; EGT's have always read low.  
Leaning cruise fuel mixtures to the verge of lean surging will only show 700C; I 
could do this to my car, and my exact same EGT model would easily show 800C+!  
That's a different of over 100C!  This is why you should "calibrate" the EGT 
gauge readings on a dyno.

Now, once you know what your safe EGT number is, we need to explain the relationship 
between lean and rich.  The engine has a narrow window to which the EGT is pretty 
stable.  We are primarily concerned with WOT (i.e. best power) EGT numbers, so 
we'll concentrate on that.  At "best power", the EGT number should be pretty 
stable.  Going leaner than best power will raise EGT - the dyno should also 
show the engine LOSING POWER.  This is due to inaudible detonation.  If we go 
leaner, EGT will start to skyrocket and detonation is pretty evident.  From best 
power, if with richen it up, the EGT will actually go DOWN for slightly richer 
conditions.  You still get almost complete combustion, but the extra fuel cools 
everything down.  If we richen it up substantially, it'll come to a point where 
all the extra fuel will start to ignite out the exhaust port, and this will cause 
the EGT to rise (this looks exactly like lean!) and sound like detonation, because 
the excess fuel is igniting in the exhaust system; this is when too rich will also
raise EGT.

Now, on top of everything, there is a delay in the response of the EGT.  REMEMBER 
THAT!  O2 sensors (narrow and wide) will react pretty quickly, but the EGT reacts 
significantly slower...and you need to keep that in mind, especially when tuning 
fuel controllers and stand-alones.

With that in mind, these are the SAFE numbers I target until I can verify (with a 
dyno) that you can go hotter...

EGT probe in downpipe, 700°C
EGT probe in turbo exhaust manifold, 740°C