Xnest:

Tests run:  65  50 Pass, 4 Ignored,  11 Failures,  19 Known Failures
246.10user 20.74system 7:49.55elapsed 56%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (2major+3285389minor)pagefaults 0swaps

Xephyr default size window: 

Tests run:  65  30 Pass, 4 Ignored,  31 Failures,  19 Known Failures
146.82user 14.36system 6:05.94elapsed 44%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+1677240minor)pagefaults 0swaps

Xephyr properly sized window:

Tests run:  65  49 Pass, 4 Ignored,  12 Failures,  19 Known Failures
242.73user 15.33system 7:47.29elapsed 55%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (2major+1981933minor)pagefaults 0swaps