Well, the x11 is basically the algo of qubit, with the algos of quark, but without the randomness of quark, so being extremely naive I'd expect the hashrates of x11 to be somewhere between the two (but closer to quark since it has more hashing algos). So if we look at the hashrates of quark with sph-sgminer, it gets less than x11 (for equivalent scrypt hashing), and x11 gets less than qubitcoin. Also, if you look at both quark and qubit, there are reports that it runs at lower temps too. So it isn't something that just affects x11, but seems to affect the other coins that use some of the algos that x11 uses.
https://bitcointalk.org/index.php?topic=475795
http://forum.qrk.cc/thread/1732/quark-gpu-mining
I have to share, which is my opinion for now, that your logic can be misinterpreted.
Quark has 9 rounds of hashing, with three of them being random. This is chosen by an instantaneous choice depending on the result of the previous hash -- i'll assume it adds 0 time in comparison to the amount of hashing done due to it being an if/else argument.
Qubit has 5 rounds of hashing.
x11 has 11 rounds of hashing.
Assuming more work must be done to complete 11 hashing functions than both 9 or 5, you would expect the time taken to complete the x11 hash to be lower than what it would take to hash either quark or qubit.
This should manifest in an overall lower hashrate . . not something between. This is not the case, as Quark has a lower hashrate than x11.
The only reason for this I can think of is that blake, bmw, groestl, jh, keccak and skein collectively take much more time to compute than luffa, cubehash, shavite, simd and echo . . otherwise those three extra random functions chosen from the pool of the same blake, bmw, groestl, jh, keccak and skein would result in a higher hashrate than darkcoin.
Without data pertaining to the time each function takes individually, I can't really take this much further. What I can point you to is that these functions are not designed to be memory intensive.
Without the intense rewriting of RAM you get in Scrypt, your card is effectively doing much less work. Note that VRM temps with Scrypt are generally higher than core temps . . while VRM temps with these algos are generally lower than core temps.
That is where your power saving is coming into play - you're not using the extra power that Scrypt burns in using RAM . . not that the miner isn't optimized . . just that the hash function itself isn't designed to ever fully utilize your GPU's capabilities . . and never will be because that's what Sha 256 and these chained algorithms are designed to do.
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