For the most part, the design of the airplane is far less important than the accuracy of the construction and alignment, the effectiveness of the engine and prop, and the state of trim of the airplane. Even a slight trim defect can completely wash out any design differences, same with the engine and engine setup. So, ultimately, the results will be determined by how well you adjust it. Search through the archives, and you will see example after example where a tiny trim adjustment took and airplane from a dog to a hero.
Having said all that, there's no doubt that the SV-11 is a much better design. The Strega goes back to the Patternmaster, with some changes. The Patternmaster can certainly be made to fly well but it was a function of a very brief period of time, and some rather extreme design concepts and a brute-force approach to stunt, create a "immovable object" (i.e. a super-stable system (for the day)), then create some overwhelming forces to make it turn. It was, ultimately, a dead-end approach but they tried every variant and the Patternmaster was the ultimate result.
The SV-11 is a conventional design that has evolved over many iterations with slight changes to accommodate observed shortcomings. There are a few things I would do differently (and do) but it has an enviable contest record and flies well for many different people. It's not extreme, it can be trimmed using modern trim techniques, doesn't require extreme power solutions, and doesn't take two hands to corner.
The SV-11 is a carving knife, the Patternmaster and derivatives like the Strega are broadaxes.
Brett