I havn't compared it directly to the 10X4........though I have tried one on an SMEIV fitted to a PT Anniversary and an Export.
I didn't like the sound at all,though this could have been down to the SME Arm
The 10x5 fitted to my Annie/Kuzma Stogi Sounded excellent.
Interesting, i had my x4 on an akito, that sounded ok ish but not astounding.
Stuck on an RB300 and it shone x4 on last legs now, but still giving some good tunes.