Whikle most of the filters mentioned will do the job, I like to look at how I know things tend to run. We rarely go to smaller tanks but far more of us go to larger. Also filters can easily have less flow than rated. It is almost a given that the flow will be lower than rated for many reasons. But whatever the rating, we tend to hang things on the canister filters that also make the flow lower. If the budget allows for the reasonably small difference in the 2215 to the 2217, I think you will be well served to go with the 2217 now rather than a smaller filter. Part of the Eheim manuals do state that it is fine to cut flow by leaving the cutoff on the output side closed a bit. No harm to motor, etc. as that is old school motors, not mag drives. I find 2217 is right for my 75's.
In going larger ,you will be covered for cutting flow if wanted, covered for later larger tanks and the price is often not that much. I do encourage looking around really carefully for the best price/shipping combo as it varies and changes often.
