Hey Bribie,
You may already have thought about this and be doing those 80°C & 65°C cube additions for extra reasons, but ... the reason i thought everyone was dropping to those temps is to reduce the volatilising off of the hops oils (most of their boiling temps are between 60-72°C, mentioned earlier here, i think).
That is, the water/wort may not be boiling, but the oils are effectively "boiling"/volatizing off into the air & disappear before they can be captured by whatever wort chemistry is also going on and incorporated/"locked" into the wort.
On the up-side, the higher the temps, the better that "incorporating" chemistry should be working.
Hence you get the tricky choice of high temps giving lots of losses but what's there gets well incorporated; or low temps giving much lower losses but less effective incorporation.
However, if you chuck your hops into a cube then seal it off, those oils ain't going nowhere!
So you *should* be able to rest assured you're getting maximum incorporation of hops oils into your wort - also both in terms of having the wort at high temps for a good hour or 2, plus at medium temps for several hours. Therefore getting almost no losses and maximising the "incorporating" chemistry.
I'd stress heavily that this is a simplified way of looking at what should
theoretically be happening. Basically i could be wrong, but i believe it's right. There's also other considerations, like exposure to hops polyphenols, etc that don't make it the only "best" way to optimise you hops oils.
Apologies for stating details you could probably be teaching me
but i just wanted to get down the background of what i now do.
So on the basis on all my theorising, what i do (for pellets) is fill the cube and at the last second throw in the hops and then quickly seal it. This is on the basis that it takes me a few-to-several minutes to fill the cube, during which i could be losing precious hops oils.
Thus far (done on the last 3-4 brews), seems to work very well to get great impact from hops oils.
No side-by-side comparisons, so i can't vouch for it being "best", but it seems pretty damn good to me.