Another vote for the custom exhaust at your local shop with magnaflo mufflers. Significantly less expensive.

sound wise...hard to tell without actually hearing it...and then it's too late if you don't like it. But I would think if the guy is good, he's probably done lots of them - maybe not to X5's but to similar size cars. Ask him if he could give you a reference to a customer he's done with a similar setup.