To the post above, Redback and H75 user here... I'll first I've listened to dozens of clips between all of these speakers and have had most of them in my cabs as well, but take this with a grain of salt.
Clips: I seem to really like the RI GB's in clips the best. The clips I've heard of the Redback have been inconsistent; some sound great and others not so much. K100, V30, Cream 90s, 65s, 75s all have been pretty consistent to my ears. I really like clips of the H75 as to me they seem like a good blend of a V30 and RI GB...to my ears. I don't find they mids hollow like a T75, but just a bit less full compared to some others.
The more I listen to V30 clips, the more I realize that on their own they could be a bit annoying, but I have them mixed with an H75 in my 2x12 and for live shows, that pair kills it. Love my tone with that pair and it cuts through the mix great.
Never liked many clips of the K100s and I don't care for them in person. Played them through many amps: Helios, Splawn, Henning, Mesa JP, Friedman, modded Marshalls, and I just don't dig them.
In-person: I love the Redback. I just did an A/B of the Redback in an OS 1x12 Voltage cab against my Friedman 2x12 with V30/H75 mix, and it more than held it's own. I was quite surprised how this comparison did in the room to my ears based on comparison clips online. It was much better in person. The Redback had just the right amount of rolled-off highs that I want and can use my EQ more to taste vs the V30/H75 where I'm rolling back Presence/Highs at higher volumes. The Redback gives me a bit more control. The bass bunch is full and tight! The Redback mids aren't flat to me, but more relaxed than the V30 and I feel slightly 'thicker' than the H75, but not as thick as a Cream M65.
I want to try the Redback/V30 mix sometime. I think you could do well with an all Redback 2x12 or 4x12. Of course, many amps are speaker and cab dependent. My 3 amps right now are modded Marshall types, and the Redback loves them all.
Regarding Redback vs. K100, since I'm just not a fan of K100's, my bias is obvious. I'm sure K100s rock in many applications, but I give the edge to the Redback based on my experiences.
Cheers.