Don't see why you would get an offroad x pipe and no tune. Kinda defeats the purpose. You'll be dumping lots of fuel and will have no power gains, which is the only benefit of taking off the cats, and dollar per hp probably one of the best mods.
As far as o2 extensions, don't mess with them, period. Too many issues with them. You o2 sensors can be disconnected from the trans housing to make them longer. It takes 2 minutes to find it, reach it, and remove it.
With LT's there is a bit less back pressure, and on a boosted car you will actually be running less boost, but still making the same power, if not more. As far as a drop in compression? You were misguided my friend. I have LT's and I can assure my car did not lose any power when I installed them