DX11 is a super set of DX10.1 which is a super set of DX10. You should have DX11 installed, DX10 games will only use the DX10 instruction set contained within it so you wont get a performance hit, it will run just like you only had DX10 or DX10.1 installed. There are also currently no games out there that want DX11 so having DX11 installed rather than DX10.1 leads to no difference at all right now so just leave your DX11 install alone.
There are already games that have been released to take advanage of DX11; BattleForge is one of them. Back to the point: As previously stated DX11 includes DX10 and DX10.1 libraries which will be used in accordance to what your video card supports. Since your video card uses DX10.1 it will use the DX10.1 library just like Windows Vista. You will not be able to use DX11 unless you upgrade your video card.