You may find some of these articles helpful.
Dual Flush Toilets Compared
Toilet Shopping Pointers
Short Summary of 6L Toilet Comparison Tests
34 Page Comparison of 6L Toilets
Seth's Rant on Crappy Crappers
There is some excellent evidence that the Australian "wash-down"
toilets provide excellent flush characteristics PLUS much reduced
tendency to clog the household plumbing lines.
Results of Caroma Retrofit Project in Western Canada
Hope this helps.
Mr Fixit eh