Decided to run QEMU's test suite on PCem, and noticed some differences.
test-386 and test-486 both crash in PCem saying invalid opcode, where they run successfully on Bochs/QEMU/DOSBox/My Machine
test-fpu does run, but there are some differences in the results.
Note that i was using this compiled version on Vogons:
http://www.vogons.org/viewtopic.php?t=38447#p371672
Perhaps at the very least you could use the results for fixes or reporting inaccuracy to QEMU
EDIT: So that invalid opcode comes from the x87 0xDF REG4 which isn't handled by the switch case.
I threw a case entry there with a pclog TODO, the rest of the tests then run.
There are quite a bit of differences between PCem when compared to the other four, although when the other three are compared against themselves, only 2-4 fpu differences