Not side by side but my take is the Dark Ride is lighter and darker sounding, would sit lower in the mix (live or studio) where the Sweet has a higher pitch, in fact the one I played next to an A Sweet Ride, the A was lower pitched. I like and use K's but actually like the A Sweet Ride better.
I don’t have any experience with the sweet ride but I do have a 20” K Custom Dark ride. Let me put it this way... For a rock gig, I could get by with the K Custom Dark but I’d opt for my 20” K ride instead. For just about anything else, I’d choose the K Custom Dark over the straight K.
Don’t know if that helps any... basically, that K Custom Dark is a great, very versatile cymbal.
My KCDR 20” is my go-to ride for big band and louder jazz combo/light rock gigs. I saw it at a drum show...tapped on it...walked away...went back...tapped on it....took it off the stand and took it to the dealer and said “I want THIS one.” That was quite a few years and hundreds of gigs ago.
I have both, and each one works very well for me. I have a newer KCDR. For me, Zildjian got it right with these two. The 20" KCDR is higher-pitched (but not high-pitched, if that makes sense), with a tighter "ping" and less overtones than the 21" KSR. Both have a great bell, good definition, sits with a somewhat lower pitch, and are adequately crashable. The medium thin weight works for each. If I was reduced to two rides, these would cover it for me. I play a wide variety of styles (not bebop or Latin) and couldn't be more pleased. I still have a 21" K Custom Hybrid ride which is heavier (medium weight) and pinger than I like, unless I'm playing louder rock.
I've had the 21" K Organic (nice bell, too dry for me), 20" K ride (good definition and bell, not very crashable), 21" A Sweet ride (good definition/wash ratio, but too bright/high-pitched), and 22" K Custom Dark Medium (Cindy Blackman-endorsed(?), should have kept this one). I've let all of them go, and - excepting the 22" KCDMR - don't regret it.
I'd take a K Sweet if I got a good deal, sure. But my 20" KCDR is without doubt my favorite piece of metal. Both as a ride and a crash -- live and in recordings -- I love playing it and hearing it. It sits so nicely just under the vocals.
KCDR is generally pretty nice for a lot of things. Had one long ago, but I gradually moved to a few other models. But if I’m using a 20”, I typically use one of my old As or my orchestral ride...I prefer those for me.