You want to consider range and data rate together when laying out your wireless LAN. Because the frequency band used by the IEEE 802.11 standard has strict and relatively low radiated power limits, you'll get longer ranges at lower rates and higher rates at shorter ranges. If you're in a relatively close-range office environment with clear lines of sight between stations, you can expect to use the highest rates. If you're in a large warehouse with metal shelving and supports to bounce signals around, you might need to limit your LAN to the lowest rates to get reliable transmission over the entire area.
Separate from the raw transmission rate, the achieved performance of your network will be affected by the visibility that stations in the network have for other stations. If you use an ad hoc network and some stations are hidden from other stations by blockage, you might incur a 40 percent performance hit. Networks using access points require visibility only from the station to the access point and thus aren't vulnerable to that problem.