I'll again repeat my points:
1. You can't put too much into the tire calculator
2. 18s do handle better (again IMO from personal experience)
I guess you overlooked the part where I said that I was referring to how the car handles - not speed - that's another discussion entirely.
My car was a daily driver that I drove in a spirited fashion - not autoX. Taking turns and offramps with my suspension, the 18s had less body roll and felt more responsive.
In addition, my car was in fact faster with 18s because I went from heavy 17s to lightweight 18s.
