Well, Tegra 3 *is* faster on Custom ROM...
HTC One X Tegra 3 TrickDroid ROM...
It is faster on a benchmark... which is not the real world
That is the problem with multiple cores. Unless you are using threaded processing a lot, the extra cores contribute little to real-world performance. However, in benchmarks, more cores can make a HUGE difference.
An analogy is: There is a 25% faster two-seater car vs a 25% slower four-seater car, both owned by people who use them daily and have no wife/SO/children/etc and do not carpool. 99+% of their time, the two-seater will have a superior amount of people-moving performance- one person at a time could get where they need to go faster. But in the rare case you need to move a lot of people, the four-seater car will have much more people-moving capacity- although it gets where it is going slower, when it gets there it has done twice as much work for you; the two-seater would have to make two full trips.
So which is better? Answer: It depends on how it is used.