Contemporary of the SPARCstation 5, but architecturally superior. The SS5 was essentially a SPARCstation 4 with a faster processor. The CPU did not have a L2 cache, and if I recall correctly, hung directly off of the SBus, crippling performance.
The SPARCstation 20 used the MBus, like the SPARCstation 10, insulating the processor from the slower SBus, giving it a fast path to main memory, at the cost of high memory latency. The SS20 supported up to 4 32 bit SPARC processors with up to 1MB of secondary cache apiece, a real speed demon in its day. I believe it supported up to 512MB of RAM
Also of note, the SS20 was the fastest (Sun-produced) machine to run the BSD-based SunOS 4.x. A few stubborn customers hold onto them to this day.