I like lines 3 - 3.5 X rod lengths.

I've been casting a lot of different rods and lines this summer a whole lot!
Even this one line that had a 95 foot belly section that was a work out!

But those lines with 60 -70 foot belly section cast nice on the proper rod.
All the new lines for all those trout spey rods are turning heads!
Hardy Mach series and SA Spey Short Heads are making trout spey thing happen!