on both machines:
-j7
server/3 = AMD Athlon(tm) 64 Processor 3700+
client/4 = AMD Athlon(tm) 64 X2 Dual Core Processor 4800+

commands: time/genlop -t

client with lzo:
emerge distcc  17,32s user 11,45s system 85% cpu 33,662 total
     Sat Feb  2 19:55:06 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 31 seconds.

server with lzo:
emerge distcc  14,68s user 7,64s system 79% cpu 28,130 total
     Sat Feb  2 19:03:41 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 26 seconds.

client without lzo:
emerge distcc  17,93s user 11,33s system 93% cpu 31,239 total
     Sat Feb  2 19:58:32 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 28 seconds.

server without lzo:
emerge distcc  14,83s user 7,77s system 78% cpu 28,764 total
     Sat Feb  2 19:07:13 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 27 seconds.

client without distcc:
FEATURES="-distcc" emerge distcc  18,13s user 10,93s system 95% cpu 30,447 total
     Sat Feb  2 19:59:45 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 28 seconds.

server without distcc:
FEATURES="-distcc" emerge distcc  16,21s user 7,55s system 71% cpu 33,053 total
     Sat Feb  2 19:05:12 2008 >>> sys-devel/distcc-2.18.3-r10
       merge time: 31 seconds.