The wires will not really do much, but look good, and give slightly higher ignition voltages, due to the fact of lower resistance.
However, they will cause slightly higher static on the radio. NOthing major, but it is noticable sometimes.
As for the precats, you will not see any real gains either, due to the flow of the other cats behind them. It could cause some catalyst codes, depending on how you cut them out. I do not recommend this course of action.
Best to ya, c4c5