Hey OP do you have a kill-a-watt you could purchase locally. If you are in the states Home Depot and Lowes carry them. If you can find one locally I am sure we could get together the 3 or 4 BTC to get some accurate power readings.
The kill-a-watt brand doesn't appear to be commercialized here in europe, and I've been searching for an equivalent device locally each time I've had a chance to head out to a store for the past couple of days, but no luck so far.
I also took a stab at modifying DiabloMiner and managed to get it to use 16component vectors, which is what GCN is supposed to be tuned for, but performance isn't what I expect and its really hard to profile/debug the tahiti since I could not find any development tools that specificly support it yet.
Wait wait wait. Are we sure uint16 is such a good idea? Last time I tried >4 (which was before 2.6, btw, I haven't tested with 2.6), it would crash in the compiler. Also, does anyone have a count on the number of registers per CU? There might not be enough registers to handle that.
Also, check some of the larger -vs, -v 40 is two sets of uint4 and -v 44 does three uint4s (unlike cgminer, -v 4 does two uint2s).