I hit Track's (GEA) 350 X Drive Prospec 8* and it felt great. Had a GD CP02 shaft. Contrary to the above, this head appeared a shade closed to my eye.
The 390 X-drive on the other hand was probably the worst driver I have ever hit. Nothing ever felt like it was hit on the sweetspot...definitely different than the 350 that would give a good "crack" on impact. Low trajectory as well.
I am looking forward to some comments about the new J33R.