IMHO, the best advice you've been given so far is to get the 6600GT (you'll need the AGP version - NOT the PCI-Xpress flavor). But the possible downside of this approach is that, due to the size of your your investment in this card, it will somewhat lock you into future motherboards having an AGP slot.
But if you decide to go for a cheaper video card, keep in mind that the TI4XXX cards mentioned above are Direct X 8 (DX8) cards - not Direct X 9. This could be a negative re other modern games and even some games that are 12-18 months old.
Since your original post mentions "mabey shorten video reincoding time", it certainly would make sense to thoroughly investigate the overclocking potential of your motherboard/processor combination.
I suggest you do the following (1) Download CPUID from
http://www.cpuid.org/index.php
Run it, select the "CPU" tab, and report to us what the "family", "model", and "stepping" are for your processor. And hope for "681".
I have looked at the manual for your motherboard and it MAY have the overclocking features you need, but the manual is not clear. Find the option labeled "CPU clock" which appears as an option under "Frequency Control" in your BIOS setup (it wouldn't hurt to read your manual or download one from the link you provided and read it) and let us know what options are available for this particular feature. But don't change anything in the BIOS - not yet.
If you go forward with overclocking, at some point it would be helpful to know what heatsink/fan arrangement you are using on the processor.