Photoshop CS4 Running slow when using 16 bit on MacPro 6 GIGSram

[Snook]

Hey guys, I have a MacPro with 6 Gigs of ram running CS4 When trying to work with 16 bit files the repsonse is pretty jerky and a PTA!!
I also have a MacBook Pro with 4 gigs and and iMAC 24 with 4 gigs and Both Run WAY faster than My MacPro with 6 gigs??
I have tried changing the % of RAM used from 70 -80 -90% and nothing really changes. The max for CS4 is 3 gigs and I have 6.
I also have several scratch disk set up each with well over 60 gigs free space.
Can anybody suggest waht I should do to get it running snappier.
I have been really happy with it on a MAcBook Pro but with the MacPro it is tather sluggish!!!!
Any help would be greatly appreciated
Thanks in advance
Snook

[rovanpera]

See if disabling OpenGL in the PS preferences helps...

[Snook]

See if disabling OpenGL in the PS preferences helps...

Thanks I will try it out and let you know..
Snook

That seems to have done!!!
Am I loosing any other advantages.. I noticed that un clicking that makes the pan move like the old CS3 instead of gliding across.
Is that the only thing it really effects?
IS that more for 3 D stuff and why would it slow down the performance soo much. I thought I had a pretty fast machine...? Maybe my graphics card is not top of line.
Thanks for the info and any further information would be great.
Even with GL on my MacBook pro nd iMac on the computer runs smoothly, it is just the MacPro that gets sluggish.
is that have to do with the Video graphics card??
Thank you
Snook