I replaced Riff Raffs with MQs in an Epiphone SG - so I spose I better respond!
My Epi SG was very hard/bright sounding, and after the initial "oh yeah :D", I actually found the MQs "too much" in that guitar.
They did the same Angussy stuff as the RRs did, and they were "instant early Black Sabbath", they seemed a lot more versatile and responsive to pick attack and volume controls. But I had to turn down treble and gain on my amp models.
The Riff Raffs went into my, then new, Gibson Explorer. They sounded loads better in there than they had in the SG. Then a few string changes later, the pickups swapped again - RRs back to the SG, the MQs into the Explorer, just as an experiment. My MQ/Explorer combination turned out to be a marriage made in heaven for me - unlikely to change.
The SG (with RRs) went back in the attic!!!
Finally, a few weeks back, I gave in to the whisperings in my head and tracked down a decent, resonant, Gibson SG Faded. Put the RRs in her, and I've been playing little else since... :D
Comparison of RR and MQ?? (Bear in mind this is based on them both being in the Epi SG [hard/bright] and the Gibbo Explorer [dark/warm/resonant], over a year ago, before I fully conquered pickup height adjustment to my satisfaction).
I found the MQs possibly more powerful than the RRs - they push my amp models harder when in the same guitar.
The RRs are "tighter" sounding, I tend to describe the MQs as "hairy" in comparison - not sure if that'll help :lol:
In my Epi SG, the MQs were too bright, the RRs "ok".
In the Gibbo Explorer, the RRs were "nice" but actually a bit weedy, not a lot of distinctive character to the sounds coming out of the speakers - but I only found this out when I put the MQs in instead. The MQs in the Explorer sound "more", a lot more expressive.
.... I think, for me it would all depend on how does your SG sound accoustically? If it's quite bright/hard, "harsh" even, then the MQs are going to take all of that and stick it straight through your speakers - much more than the RRs do - that might be what you want? :lol:
It wasn't what I wanted, I was expecting bluesier, not more mellow maybe, but something along those lines. I didn't get it in my SG - I got blistering top end and upper mids... very nice, but a bit much for me all the time :lol:. But in the Explorer, boy-oh-boy, my MQs are just what I want - like Twinfan says, hot, fat and warm... but they have the bite to get through that massive lump of mahogany. The RRs only seemed to cut through with the top end, they seemed to leave the detail in the lower end and mids behind on my Explorer!
Sorry that rambles a bit... not sure it will help, but I hope it does a little.