There's another current thread about tanks & no of spirals, I have the full range of Paterson System 4 and won't use the largest, they are too weak, andI had one split some years ago.

Go for the ones that take 2 or 3 120's, the plain System 4's are just as good.

Don't bother with the Systen II ranks, I used them at school, they are OK but the 4 series arevastly superior, I used to use the Multiple Series II tanks for E$ because they weer far more economical on chemistry, I still have maybe 7 or 8 of these older tanks.