The paper investigates the revenue and efficiency of different ascending price auction architectures for the sale of three items and five bidders. Four architectures are studied:  two different sequences of single item auctions, simultaneous auctions with a common countdown clock, and simultaneous auctions with item specific countdown clocks.  A countdown clock measures the time until the auction closes but resets with each new bid. The environment contains independent private values, no uncertainty about own preferences, no information about other's preferences, and a one unit budget constraint. The Nash equilibrium best response with straight forward bidding fits both dynamic and outcome data well.  When non-unique Nash equilibria exist as in the case of simultaneous markets with a common clock, the social value maximizing Nash equilibrium emerges as the equilibrium selection. Both total revenue and efficiencies depend on the architecture as predicted by the Nash model, with the exception of the independent clocks architecture, which performs poorly on all dimensions.