There have been proven gains on the focus to show that it does gain power albeit small if still using a shorty header but bigger ones mainly due to the whole manifold being replaced by a long tube header, on the SVT removing the stock cat will not gain hp but you will gain tq has that motor is already pretty much maxed out from the factory. Just like the myth that a bigger exhaust will make you loose power as well is also false (for our cars at least) 3" exhaust has been shown to be the best, that's why we recommend 2.5" or bigger. Loosing power due to the O2's not being able to meter right is just boloney. Please read through our performance sticky threads before posting any other false information. Not every car is the same so don't assume that what goes for one car works on ours. Also when removing the cat it is a must to get a tune to correct any problems that may arise from the deleting it (like the CEL) plus it optimizes any other mods done to the car so you get the maximum benefit from them.
Performance sticky threads HERE