Will I benefit from installing the DX11 upgrade if I only use the "very high" graphics setting? [It is next up from the default "high".] Or do I have to use the highest graphics setting to see the DX11 features?

BTW: I have...
Windows 7 x64
4 GB RAM
NVIDIA GTX 460 768 MB

It depends are you planning on enabling high resolution pack ?
If so then objects need to be set at ultra ,can't remember if extreme works too ,but below that
displacement mapping doesn't work , it's just flat texture.
I don't now about other DX11 features. (didn't test it out yet)

And why would you say now that you only gonna set it to very high?
I think you should test if higher settings will work too.
maybe not all ultra but at least maybe objects for above reason and the rest can be set
lower.
Your call.

Also which cpu do you have?
And which driver are you using for your videocard.

Current out is : 280.26 Whql certified
It increases performance with crysis 2

only ultra has any noticable DX11 effects.
if your resolution is very low (like at or below 1280x1024) you should be able to run extreme comfortably.

Off topic...

Question, does it improve your vision for stealth guys (without using nanovision) on ultra settings with directx11 (sadly I can only run crysis on high graphic settings)? I notice some of the players here with high end specs can spot stealth guys easy.

regards,

^I think all the settings look very similar. you have to actually stop and stare in order to distinguish between them. so yea doesn't make that much of a difference. heck u may even have a slight advantage on high since there is less going on. also i heard somewhere that there are commands to make stealth easier to see?
I usually play MP on extreme for performance and SP on ultra for quality.

and fri13th, since ur such a good player, why not invest in some hardware to improve your experience?

Yeah, but i'm planning to upgrade my PC next year since my pc has still enough power to play high end games. Fyi my cpu and gpu specs:

CPU: Intel Quad Core q9550
GPU: ATI HD Radeon 4870

Unless the winners from the tournament donate their cash price for poor me who couldn't play crysis 2 on dx 11 lol