I've got some Zardoz Notwax on order to see how that compares. F4 was the most promising liquid wax I found at REI in Troy.
Coming down South Hill on the Spring Lake trail was DEFINITELY faster with the F4 on the skis than without. I'm still struggling to make the first hard right turn at the top of that hill with my 215cm skis. I'm sure I'll get it one of these weekends!