However, as noted below, it appears that the slowdown does not follow the client VM.
I don't know the cause of this slowdown but for the time being, am recording this as a javac issue.

Below is a script that is called from inside a langtools/ dir with the path to a jdk. It will compile all the .java files under langtools/src with the given compiler, once with -J-client and once with -J-server.

Below are times I have observed running in a langtools clone with this tip:
    changeset: 1475:a9cb93cca229
    tag: tip
    user: jjh
    date: Mon Jan 07 17:51:05 2013 +0000
    summary: 8005647: langtools/test/tools/javap/MethodParameters.java fails on windows

These times are seconds reported by the bash 'time' command:
........................windows.32..........solsparc32
.......................client..server.......client.server
7u9......................7......14
7u10............................................25....43
8b55.....................8.......9
8b55,.b69.client.....8......10
8b69:..................10......12.............41....46....


- win machine:
    Core2Duo, 2.8GHz

- solaris machine:
    System Configuration: Sun Microsystems sun4u Sun Blade 2500
    System clock frequency: 160 MHZ
    Memory size: 2GB

    CPU Freq Size Implementation Mask Status Location
    --- -------- ---------- --------------------- ----- ------ --------
    0 1280 MHz 1MB SUNW,UltraSPARC-IIIi 2.4 on-line MB/0
    1 1280 MHz 1MB SUNW,UltraSPARC-IIIi 2.4 on-line MB/1
=======================================================

#!/bin/bash
mkdir -p fred
rm -rf fred/*
find src -name \*.java > fred/allJavaFiles
echo
echo $1 -J-client
verbose=-verbose
verbose=
time $1/bin/javac $verbose -d fred -J-client @fred/allJavaFiles 2>/dev/null
echo ==============
echo
echo $1 -J-server
time $1/bin/javac $verbose -d fred -J-server @fred/allJavaFiles 2>/dev/null

exit