I have ran both 3:55/26" tires and 3:91/27" tires and I like them both with my 340/727 Challenger. I don't usually run 70+ (except WOT runs) but up to 70mph cruising speed is fine with either of these combos.

1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)