(* http://stackoverflow.com/questions/8374056/is-it-safe-to-turn-off-patternpatv *)

In[1]:= SetOptions[TimeAv, Method -> {"MinNum", 400000}, "BlockSize" -> 20000]

Out[1]= {Method -> {"MinNum", 400000}, "ClearSystemCache" -> False, 
 "BlockSize" -> 20000, "StoreAllTimings" -> False, "PrintStats" -> True}

In[2]:= Clear[f]
        f[{x_, ___} | x__] := g[x]

During evaluation of In[2]:= Pattern::patv: Name x used for both fixed and variable length patterns. >>

During evaluation of In[2]:= Pattern::patv: Name x used for both fixed and variable length patterns. >>

In[4]:= {f[{1, 2, 3}], f[1, 2, 3]} // TimeAv

During evaluation of In[4]:= Total wall time is 2.580774, total cpu time is 2.37615 and total time spent evaluating the expression is 2.37615

During evaluation of In[4]:= The expression was evaluated 400000 times, in blocks of 20000 runs. This yields a mean timing of 5.94037*10^-6 with a blocked standard deviation of 1.11362*10^-7.

Out[4]= {5.94037*10^-6, {g[1], g[1, 2, 3]}}

In[5]:= Clear[f]
        f[{x_, ___}] := g[x]
        f[x__] := g[x]

In[8]:= {f[{1, 2, 3}], f[1, 2, 3]} // TimeAv

During evaluation of In[8]:= Total wall time is 1.472172, total cpu time is 1.47209 and total time spent evaluating the expression is 1.47209

During evaluation of In[8]:= The expression was evaluated 400000 times, in blocks of 20000 runs. This yields a mean timing of 3.68023*10^-6 with a blocked standard deviation of 9.79857*10^-8.

Out[8]= {3.68023*10^-6, {g[1], g[1, 2, 3]}}