howdy,
I am reccommending the platforms plus powergrips based on a good amount of long distance riding and experience... I used to wear sidi dominators paired with time ATAC alium pedals, which were very good. However, I got hot spots about 8-10 hours into brevets with this setup, and would occaisionally (overnight rides or cold wet weather) get a sore knee. After faffing around with microadjusting the cleats, I found that slight periodic readjustment during a ride would relieve my pain... for a while, then i would need to slide the cleat back to the original spot.
After reading kent petersens rationale behind powergrips for his race down the continental divide trail, I was intrigued. I found this pedal setup allowed me to shift my feet forwards and backwards slightly, thereby releiving any pain I experienced.
I still use the sidi's and clipless for mountain biking, but not long rides...