I always play with strength 5 indies... much more fun, IMHO. You actually have to prioritize your conquests, and indy battles are dangerous! Some provinces never even get taken (like ones with 80 units of mixed knights and longbows).
Playing with higher strength is even
more fun, but sometimes there are odd effects, like a Dom I game I played with strength 7 indies, and a couple provinces started with commanders with soul contracts... by the time I got to them, they had upwards of 50 devils...
-Cherry