The key difference between the 811 and the APC new standards is that the 811 is a true straight leg while the APC is slightly tapered below the knee (811 also has a higher rise front and back). I prefer the slight tapering because it gives the effect of a true straight leg and some on this board feel this gives a better look than a genuine straight leg that can give the effect of a slight boot cut. But I don't like the low rise on the APC.
The 811 is slim in the thigh, it just continues on straight. I've got the 34 and the 36 waist, and when I can fit into them the 34 is the better because of the narrower leg. But you have to wait a while for some stretching.
Agree with everyone above, I find the 811 an odd fit in the top block. The denim is superb, the fades are wonderful. But I find them too hot for the Melbourne summer. I note Kiya's point. If you are worried about warmth, I'd be more concerned about the 811 than the IH.