Mmm, maybe four. I also found three a challenge on one of my emerald playthroughs, but in fairness I hadnt been grinding and my team was insanely underleveled.
Six was by far the easiest, barely even registering as a challenge. I actually didnt find seven too bad either; I had to retry once because I didnt bring in enough potions, and then again because of the champions darn snorlax.