True, side pipes are nice but not everybody's got a Cobra you hoser!
I'm a jealous man!!!
If you just want loud, go straight pipes, no h, no x, no mufflers. An h crossover builds power and does take some of the chop out of the exhaust note. Hell, Ford does it from the factory, it's got to be worth something for them to add that extra piece in there. The x will probably build more power than an h crossover and it will sound different. Nascar cars run them, enough said. Honestly, I've never hear an x pipe in person, but if it's different than the sea of other hot rods out there, then it's cool in my book. The muffler and size of pipe is where YOUR CAR'S exhaust note is going to come from. As far as chambered and straight designs tied into an x or h crossover, who the hell knows!
If you want a low rumble, look for the longest and largest diameter tailpipe (assuming you use mufflers). As for power, as long as it flows, you should be good with either H or X. X being a higher RPM therefore peak power gain, but there are other ways to affect your power more than the exhaust crossover type.
I personally like the sound of 3" pipe, but it's pretty darn big out the back of your car. My buddy's truck sounds mean as hell tho.
In Car Craft they did a write up on H, X, and open headers. I was looking in the store today X pipe made more HP then open and H. I am a doofus, and did not look at the TQ numbers though. Check it out though.
Or you can fabricate them, which I did on my GT. They are 24" with 2 1/2" pipe, 4" outside. The key to mine is that they have a removable end. I can pull out the stainless perferated centerpiece and either add more packing (gets real quiet) or take it all out and get your ear plugs. It takes about 5 minutes to take the mufflers out, then a few more minutes to take the ends off and play with the packing.
Well I whould go with the X , but at least put a H-pipe on it or it will sound like a chevy truck with cherry bombs , ehawwwwww, ever wonder why chevys just dont sound as good as that "5.0" sound everyone wants , I think the H/x pipes make them sound smoother and less ratty , not higher pitched , my '65 just had 2.5 flowmaster with turn down, then put a crossover tube on it ,torque picked up , and sounds way cooler , 3in x-pipe coming though.
Can't seem to find any links to x-pipe discussion in the archives, damn.
A couple of points from that discussion were worth noting:
1) I had the same concern about Flowmasters and x-pipe but after exhaustive research I was not able to find any facts or actual research confirming or denying a problem. I asked Flowtech what muffler type they suggested with their x-pipe and their answer was their Aero muffler. The design of the Aero is to maximize flow with no baffling (some guy pointed out he could drop a pop can through one).
2) Because the x-pipe is just a better h-pipe and Flowmasters work fine with them I really don't think a differnce would be that noticable.
3) The biggest factor in making the whole system work is in the spacing of things, particularly where the x-pipe goes. Other tricks are dumping the exhaust before the axle.
4) Because the x-pipe is a baffle it does reduce noise - but she howls like a banshee at 5000rpm.