Korbel is a medium fast all wood blade. Very controlled and decent speed. But if you are looking for a blade with which you can kill the ball look elsewhere.
I, myself, had the viscaria and currently own the innerforce layer zlc blade and it's one of my favorites from butterfly alongside the Freitas Alc. Both of these blades give you more dwell time on the backhand and have a softer feeling in general. When comparing these two with the viscaria they gave me a sense of security in hitting which I lacked playing the viscaria. Basically they are more forgiving, offer a longer dwell-time and teach you to hit through the ball more so than the vis. Don't listen to what the guys said lol + the innerforce zlc has the nicest feeling for backhand I've experienced in all of my time playing table tennis. So I'd recommend you go with the innerforce zlc. Btw don't get baited by marketing and fall for buying the Franziska version for instance. It plays A LOT worse than the regular innerforce zlc.
You play the Viscaria when you are able to handle it. Not because some dude online tells you real men use Viscaria haha
Hope this helps