| Yes, the Red Mitchell set comes in Weich and Mittel and the differences are similar to what you find in the fourths tuning sets. The Weich on my bass have slighty less pizz sustain and are a bit less harsh with the bow.
I've also run spiros on the bottom two with various others on top. Obligatos, Flat Chrome Steel, Doms, Helicores, etc... I've got a couple of Bel Cantos I've been meaning to try too. In general I love to spiros on the bottom but don't really like the arco sound on the top so I keep changing up.
The full Obligato set works well in general. I've done some nice recordings with them, but was having a bit of an issue with pitch stability on the A so they came back off.
Currently I've got a set of the Velvet Compas 180 5ths strings on and am loving them, but it's only been a month. Softer under the hand, nice warm pizz and easy under the bow. We'll have to see how long the can hang before the Spiros call me back....
If you've got the $ for the Velvets, so far they are the nicest arco set up I've had on, but I bet the Spiros on bottom with Bel Canto D and A would be really great and less money. | 
