We compute cell-wide mean throughputs for a wide range of multiple-input-multiple-output (MIMO) system design parameters, in both single-and multi-cell scenarios, using realistic models for channel dispersion, path correlations, and cochannel interference. We assume the use of single-carrier modulation, and quantify the degradation in downlink throughput as the channel dispersion increases. Our results highlight the potential harm even from mild dispersion in MIMO links. In studying path correlations, we assume linear arrays at each end of the link, and quantify the interplay among device size, number of antenna elements, path correlation, and carrier frequency. We show that, under practical size constraints, the use of additional antenna elements can be counterproductive.Index Terms-MIMO, MMSE, multipath fading, shadowing fading, co-channel interference, cross-stream interference, frequency-selective channels, interference cancellers.