How will be graphics if Nvidia 9500GT paired with Intel HD Graphics?

Hi
I've MSI P8B 75-M LX Mobo which have LucidLogix Virtu technology, where Intel Graphics wont go waste if u install discrete graphic card.
My Intel HD graphics plays most of the games, i've tested NEW NFS Hot Pursuit & Most wanted 2012 both are playable at Mid Graphics at 1024x768 @ 15-17fps
I know 9500GT is very poor for gaming but if paired with IGP. Wouldn't it be better?
But the thing i'm concern about that, my IGP graphics have DX11, but 9500GT does not uses Dx11, it supports 10. Would be there any problem? or should i go for anything Directx 11?

I've PCI-Ex x16 v3.0 in mobo.

One of my friend using 9800GT on core2duo and he had completed all the latest games even Max Payne 3.

If i buy a new 1G DDR3 graphic card probably around 4000 which will be the best?

I've Intel G645 Processor, 4G DDR3 RAM, and 17" CRT monitor.
Want to play Battlefield 3 @ mid graphics

Technically, you should get better performance if your pair up the 9500GT with the IGP. But it also depends if the developers of Battlefield 3 have catered to this. While Windows and latest versions of Direct X have taken some of the guess work away from the myriads of PC hardware that need to be supported. You can never truly be 100% sure. You will need to check the technical spec requirements for the game and maybe even visit the developer's website and/or forum. If you still can't find the relevant information, I suggest sending them an email.