Good luck with the build. I would seriously spend the extra $50 and get an ACT disk. I wouldn't trust the xtd over 450hp.
Also just letting you know that the 99 has a programmable ecu. You just need a $150-200 cable and $25 software, and you can program the ecu like the evo guys do. People have made 1000hp on the stock ecu with this sort of setup, so I know it's capable of meeting your goal.
as far as widebands I recommend the MTX-L. It's more capable the the aem wideband and the replacement sensors are easier to find. Same price too.
You might want to look at the HX40. It'll get you to your goal, and the best part is that it's cheap, rebuildable, and will spool as fast as the ball bearing counterparts.