Xorg 7 uses much more CPU than Xorg 6

[Eric van Gyzen]

Immediately after upgrading from Xorg 6 to 7, I noticed that whenever an 
xterm is "busy" (e.g. compiling something), the entire desktop is sluggish. 
  I've noticed this on at least three machines with vastly differing hardware.

To quantify my experience, I created to slices on one i386 machine and 
installed two systems:
     FreeBSD 6.2 with X.org 6.9
     FreeBSD 6.3 with X.org 7.3
I created the initial xorg.conf file with "X -configure" and made trivial 
modifications for my mouse and monitor.

Running only twm and some xterms, I compiled the 6.2-RELEASE world on each 
system and recorded the CPU time used by the Xorg server:
     Xorg 6   7.23 seconds
     Xorg 7  17.77 seconds

I also ran "yes" with an 80-character argument and ran top to watch CPU 
usage.  After top reached a steady state, I recorded the following:

==== Xorg 6 ====

CPU states: 67.3% user,  0.0% nice, 32.7% system,  0.0% interrupt,  0.0% idle

   PID USERNAME  THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
   709 root        1 120    0  5240K  4200K RUN      1:08 61.24% xterm
   702 root        1 107    0 54636K 10176K select   0:47 30.77% Xorg
   729 root        1   6    0  1260K   616K ttywri   0:04  3.28% yes

==== Xorg 7 ====

CPU states: 25.9% user,  0.0% nice, 74.1% system,  0.0% interrupt,  0.0% idle

   PID USERNAME    THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
   768 root          1 122    0 58408K 13188K RUN      1:13 71.44% Xorg
   777 root          1 106    0  5344K  4284K RUN      0:25 24.77% xterm
   793 root          1   6    0  1268K   604K ttywri   0:02  0.79% yes

================

Does anyone have any ideas why this is happening?  I'll gladly supply my 
configurations, but they are all remarkably generic.

Thanks,

Eric