I am using the 6-2+ on a 75 with 30 gal Sum/Refug. I could have gone smaller, but when I was talking to he guy at h2o he said to go with the larger pump. I think the 6-2+ or the 8-1 would either fit your needs.
With the mine, I have it set so only the real nasties make it into the cup. My foam wil usually hang in the collection cup for better than an hour if I shut the skimmer off.

My only complaint would be that when I add selcon (vitamin supplement) the skimmer stops producing and I have some bubbles escape the skimmer. I think it is because I have the skimmer water level set so low.

All I do for maintenece is clean the cup once a week, put hot water down the venturi every 2 weeks and clean the whole skimmer once a month (or 2 or 3)

Cheers,

Al