AGL Future Earnings, page-141

I agree, gas, particularly OCGT has a very high SRMC, I would suggest its over $150/MWh at current gas prices, so that effectively makes ORG gas generators basically physical cap, so yes, far less efficient, but more flexible.
AGL's fleet has an insanely cheap SRMC, I think one station is around $10/MWh +/-, they did some great coal contracts a long time ago

But that was why I mentions the spikiness of a typical days price curve rather than just the average. ORG will benefit from extreme pricing and avoid the negative day prices

as an example from NSW yesterday, having fixed generation at -$35/MWh (around mid day) cant be good for large fixed generation. and I think we will see more of that over time, just offset by very high shoulder peaks.
I would just conclude ORG is slightly better set up than AGL with flexible (but expensive) gas peakers and a relatively flexible Eraring
But of course so much can change in a short space of time, EA drops a unit here or there and/or a Callide blows up etc and we get a repeat of last Q which saw sustained high prices. I definitely think there's more risk we get higher wholesale prices than lower prices in the short to medium term. AGL would be happy to see that.
This summer will be interesting