GTX 650 Ti + KDE + two monitors - tearing and poor performance

Hi, I’m trying to back from radeon world after 2 years, I bought GTX 650 Ti OC 1GB from Gigabyte.
My other hardware is:

Two monitors:
DELL U2412M (1920x1200 @ 60Hz)
Benq 2222hdl (1920x1080 @ 60Hz)
and:
i7 2600K, 16Gigs of ram and P8P67 Mobo from Asus

Everything works nice when I enable only one display (Dell). Desktop effects are smooth. It breaks after attaching second display. I experience tearing on both screens. When I try to enable VSync in KDE options I can see performance drop. But this drop is weird. For first few second everything is smooth, but after for example few window minimizations animations become slow. After some time it’s going back to normal for few seconds then back to be slow again - something like sinusoid. When I disable vsync in KDE options everything becomes smooth again, but with horrible tearing. For me it looks like double syncing or something. I tried to set max performance in nvidia control panel, but it doesn’t help.

A can add, that I have not this kind of problems with my HD5770 on fglrx. Here both displays are synced properly without tearing, and desktop is smooth.

Maybe somebody experienced something like this or have any advice for me…

PS. I tried last stable driver from Debian repo (319) and last beta downloaded from NVidia site, both with Linux 3.9. KDE 4.10

PS 2. I found that this one is similar to mine https://devtalk.nvidia.com/default/topic/534907/linux/any-experiences-with-twinview-3-or-4-monitors-and-kde-/

Cheers, majlo.

Really, is no one using KDE with two screens on NVidia card ?

I do, but on a 9500GT card, and have no issues.
Other users reported vsync problems with gtx6xx cards and i think even on single head setup, just search this forum.