War is inevitable. The Culture vs. the Imperium doesn't end well for the Imperium. The Culture has more reliable FTL, is tactically much faster in that most battles take place in microseconds, and has more powerful weapons that outrange anything in 40k. The Culture destroys Imperium forces as fast is it encounters them.
The Culture vs 40k usually boils down to how the warp affects a Culture Mind. That generally devolves into a flame war, no limits fallacies, and just bad news.
You may want to check out /r/whowouldwin, they have had a number of interesting topics about this as well.
I don't usually read fanfic but there is a long running 40k/Culture story that is actually very interesting here.
I am not big into fanfic but I have read 2
One is this Culture/BSG cross over. Very well done I think. Be careful because it doesn't finish.
https://www.fanfiction.net/s/4190427/1/A-Day-in-the-Life
The other is a Culture/40k crossover. Also good, but very long and still ongoing (I think). You do need to know some 40k for it to make sense.
Here are just the story pieces of the culture running into 40k http://sync.in/ep/pad/view/ro.f7Ii2bq8IM01rFxsOm/latest Here's the full forum thread, with all the commentary. http://www.giantitp.com/forums/showthread.php?256776-The-Culture-v-s-40kverse
There are two more threads after that.
If your interested, below is a link to a long running 40k/Culture crossover fanfic. I don't usually like fan fiction but this one is surprisingly good.
I am not big into fanfic but I have read 2
One is this Culture/BSG cross over. Very well done I think. Be careful because it doesn't finish.
https://www.fanfiction.net/s/4190427/1/A-Day-in-the-Life
The other is a Culture/40k crossover. Also good, but very long and still ongoing (I think). You do need to know some 40k for it to make sense.
I've had similar luck. It really helps to have an "official" version.
PLUS, Google Docs has a chat so we can refer to each other if we're on at the same time.
Other similar online docs we could use are things like http://sync.in/
I wasn't very familiar with 40k and had only read one culture book and it made sense to me. That is the one though I read it originally here: http://sync.in/ep/pad/view/ro.f7Ii2bq8IM01rFxsOm/latest
Not sure which is more complete.
Git, the VCS that powers GitHub, is not particularly difficult to use, and is vital for any project beyond one or two files and one or two contributors. It is, however, not live. For that, I suggest http://sync.in/ or Google Docs, though the latter has no syntax highlighting.