From the testing we have done so far the ATI Sunpower 6 x 54w is producing right at 20% - 25% more par than the Tek Light Elite 6 x 54w, in a 48" x 18" area. Going outside of the 18" area (tanks tanks that are 24" - 36" front to back) the Elite starts to climb up in par, and eventually surpassing that of the ATI Sunpower.
We have been in communication with Sunlight Supply for the last couple of days in regards to this, and they are considering looking at a new reflector for the Elite which will give more par straight down like the Sunpower does, but less in the far outer reaches of the tank. This would give the hobbyist two options, depending upon the footprint of the system.
I also tested an ATI Powermodule 6 x 54w and noticed less than 2% lighting increase from the ATI Sunpower.
All tests were performed at 19.5" through air only, using only brand new ATI Blue Plus lamps in the fixtures. Test numbers were taken after 90 minutes of run time on all fixtures to allow them to get up to full temperature.