Anything less than ten frames in a national box and your increasing the probability of breaking the lugs quite drastically.
Ten is the ideal.
I've tried aĺl sorts over the years, now settled on commercial supers with manley frames for spun frames and national manley for cut comb, still have thousands of SN4 in the system which are gradually being replaced. It's the castleations that are a pain, literally, as I keep cutting my fingers on them.
Also we have twenty frame extractors, odd numbers wouldn't work.