There is a particularly well written article on data warehouse appliances by Doug Henschen in Intelligent Enterprise, which both usefully summarises the market today and has a very clear explanation as to why columnar databases are well suited to certain applications.

Above all, it contains an excellent piece of advice on benchmarks, which is not to trust them and to ensure that vendors test their systems on your own data. Benchmarks have a place, but vendors go to considerable lengths to ensure that their tests are highly optimised to the particular benchmarks. For example, many TPC-H tests end up being executed entirely in memory using hardware that is not like that server sitting under your desk in the office. Vendors will heavily tune their systems to ensure that their TPC numbers look good, but the data they are using may have very different characteristics to yours, and may perform very differently.

Fortunately, the explosion of appliance vendors in recent years means that there is now serious competition, so you should have no trouble convincing vendors to carry out proper proofs of concept using your own data.