Leave the two macs alone for now. Once they have leafed out fully later this month, you can cut back any bare or obviously dead stems.

Bobo and Little Lime bloom on new wood anyway so those can be cut back as hard as you like. It's a bit late for heavy pruning on these so I would leave as many stems with leaves present as much as possible or cut back very lightly so as not to adversely affect the flowering.

I've lived in the PNW all my gardening life and I have never experienced any winter dieback or cold damage on my hydrangeas. It must have gotten very cold where you are! Even the couple nights in the high teens didn't bother mine.....and they are all growing in containers.

Climate Weirding.

All of my macs look like crap, and I'm supposedly in zone 8b! In my case I think it was less the January 13 event and more the multiple freezes in late March and throughout April --after all of my macs had leafed out and started growing-- but it could be some of both. Almost no terminal buds have survived, but I am seeing cauliflower buds now on lateral shoots that took over for the dead terminals.

Oh, wow. What bad timing. I would hold off on forcing new growth by fertilizing until the stressed plants show new foliage or new stem growth; just water and mulch until then. The panicles may be preparing to develop flower buds so try do not prune hard now. If you needed to prune hard, that should have been done earlier. When I suffered a similar fate, I simply let the hydrangeas, azaleas and camellias alone for two months until I could visually see where dead wood ended and then I cut above the live growth. Rave/etc has flower buds at the end of the stems so it is best to keep the pruners away and monitor how the broccoli heads open: if they are healthy, they will be fully green. Otherwise, they may be partly brown or fully brown. The plants will decide which leaves to keep. Partly green ones are still producing food for the roots. Brown leaves can be clipped off by only cutting the string that attaches each leaf to the stem. Hope you have "some blooms" this year. Rave should produce a second flush from the new stem growth but it will usually be later on, once the stems are tall enough to trigger flower bud set and immediate blooming. PS -since Rave stays low to the ground usually, consider throwing some burlap, frost cloth or old sheets to protect it in the future; watering the night before may also minimize damage up to a point.