Linux Jerky navigation with GF210

I'm using XBMC live, I'm using the stock ubuntu drivers for everything so updates run smoothly, installed on an 16GB SSD & driving a 1080p HDTV. The system was very smooth & fluid up until I changed my graphics cars from a GTX 275 896MB to G210 256MB. With the G210 installed I'm finding that the menus are jerky & sometime pause for a moment before acting on the keyboard input, however there is no effect to any video playback even the most demanding HD videos I have play back smoothly even if the menus are being jerky over the top. This only effects Aeon Nox, Confluence & Quartz are both smooth & fluid using the G210. I'm using the stock ubuntu 280.13 driver. If anything the CPU utilisation is lower using the G210 than the GTX 275. Why would Aeon Nox be effected by the change of GPU & nothing else? For reference my system is:
* Pentium Dual Core E5200 @ 1600Mhz (4x400MHz)
* Gigabyte EP43-DS3
* 2x2GB DDR2-800
* GTX 275 896MB or G210 256MB
* Samsung 1080p HTDV
* Keysonic KSK-3205 RFM mini keyboard
* PATA 16GB DOM SSD (OS & xbmc home directory)
* 3ware 9650SX-8MI
* 8x2TB 5400RPM HDD (all video, audio & picture media)

Could the interface fluidity problem be cause by a lack of vram on the graphics card or a lack of GPU power, which to me would seem odd.