17s will significantly improve the handling of the type of rubber you describe over 16s. If you are going to invest in that rubber, IMHO it makes sense to get the wheels to support them. If you had said street, year round, all-season, I would say 16s.
18s are overkill, and the rubber is outrageous.
Based on your priorities, my initial reaction is to tell you to find the cheapest 17x7.5 ET48 wheel that you like and buy it. It probably will be under #20 which is fine for the street, and should be fairly durable.
In addition to the place that has my wheels, we have some members with a hook up with Tirerack, or discount tires I think, so check them out.
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I am a Commodore PET --- Now get off my lawn you kids...
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