David,
An oil temperature gauge would be a handy aid here. Before I added an oil
cooler I used the oil temp gauge to dictate my speed. If the oil
approaches 220 degree I would back off the gas pedal.
Try lowering your oil level a bit. With the level to the full mark the cam
whips the oil into a froth.
I am surprised the quick-fix techs didn't check the oil relief valves and
springs.  I would clean the valves(I think the WBX has two) and bores so
they move freely. Make sure the springs are the correct length, it might
buy you a couple psi.

Good Luck
Ken Lewis
http://neksiwel.20m.com/photo_1.html  oil cooler stuff