Hi Beeline,
That's a serious margin in that sort of temperature with packs and NAI on! Lets hope it isn't heavy or high too!
I read it differently. It looks like it's taking off using reduced thrust and is below thrust reduction altitude. The assumed temperature is 59 degs C, whilst the ambient is probably below +10 degs C and in icing.
Hi ImbracableCrunk,
That, to me, seems like an argument for using N1.
If you really don't want to know your effective thrust - then stick with N1.
Cockpit Design: EPR v/s N1 indication « The Flying Engineer
"The advantage with EPR is that it is a pressure ratio, and is indicative of engine thrust. Simple physics will tell you how: Force (Thrust) = Pressure multiplied by the Area of application. According to Boeing, EPR is more directly related to, and a much better indicator of thrust than the compressor speeds (N1 and N2), and therefore is more advantageous in terms of accuracy to utilize EPR to control engine operation."