Hourly averaged interplanetary magnetic field (IMF) and plasma data from the Advanced Composition Explorer (ACE) and Wind spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth have been analyzed for systematic and random differences. ACE moments-based proton densities are larger than Wind/Solar Wind Experiment (SWE) fits-based densities by up to 18%, depending on solar wind speed. ACE temperatures are less than Wind/SWE temperatures by up to ~25%. ACE densities and temperatures were normalized to equivalent Wind values in National Space Science Data Center's creation of the OMNI 2 data set that contains 1963--2004 solar wind field and plasma data and other data. For times of ACE-Wind transverse separations <60 RE, random differences between Wind values and normalized ACE values are ~0.2 nT for ∣B∣, ~0.45 nT for IMF Cartesian components, ~5 km/s for flow speed, and ~15 and ~30% for proton densities and temperatures. These differences grow as a function of transverse separation more rapidly for IMF parameters than for plasma parameters. Autocorrelation analyses show that spatial scales become progressively shorter for the parameter sequence: flow speed, IMF magnitude, plasma density and temperature, IMF X and Y components, and IMF Z component. IMF variations have shorter scales at solar quiet times than at solar active times, while plasma variations show no equivalent solar cycle dependence.