This paper studies stationary 
queueing systems with first-come first-served discipline and generic interarrival and service times T and S, respectively, both with first two moments finite and (relative) traffic intensity 
. The components of the stationary Kiefer-Wolfowitz vector, 
, 
, of workloads form an associated family of random variables. The first moments are bounded below as in 
, the bound being tight in 
systems for which 
for some 
. If 
, then there is a system for which the mean waiting-time 
. By considering the limit as 
of a sequence of systems with two-point service time distributions specified by 
, where 
, an asymptotic decomposition result is established for the sum 
amongst systems with given first two moments for S and T; it is new even for the single-server case. From this and further detailed asymptotic results it follows that when 
, amongst systems with given first two moments finite for S and T, there is always a sequence of systems for which 
. Heuristic calculations indicate the nature of all the 
when 
. Evidence concerning conjectured upper bounds on 
is reviewed.
