Aside from a trip in one my perf knowledge is limited to a brief by a TP who had the B-52 as one of his project aircraft. The cruise performance is akin to an older generation 4x civilian jet but when laden the T/O performance eats runway length for breakfast. Taking off laden with weapons and refuelling in the air is the preferred and sometimes only option.
Net takeoff flight path (or the USAF bespoke version of it) does honour the loss of an outboard engine. Loosing both engines on an outboard pylon is another matter, with some significant gaps in performance. Vmca with the loss of thrust from an outboard pylon didn't look funny at all. I can only presume that it was this that parked any of the fanciful ideas of swapping from 4 pairs of engines to 4 bigger engines.