Yes the X pipe helps, especially if its set up right. I have one on my truck and love it, just dont put 40series Flowmasters behind it....Doesnt sound good. I ended up putting Summit glass packs, because the flows were corking my system with the baffles they contain, it sounds awesome now and performs better.
The X-pipe splits the flow in the 'X' junction which balances the flow of exhaust pulses and eliminates the firing order differences between each header. With an X-pipe your exhause will scavenge better, sound better and as a bonus will quiet the exhaust out a bit. You cant go wrong with an X-pipe in my opinion. To see how it works for example get two straws normal sized and one big one from AMPM that the big gulps use, cut a 1/2 inch section of the big straw off. Now get two smaller straws and stick them in one end of the big straw you cutt off and tape them there as best you can... do the other side the same way. This will now simulate what an X-pipe will do for your engine. Now... Blow on one end... either end it doesnt matter, when you blow that simulates the exhuast. Put your finger slightly over the other straw on the same side of the X that your blowing on... You should feel some air being drawn in from the other side.... That is how the X- helps your exhaust scavenge better.
Hope this helps.