Will an ASUS hd6850 fit?

Really can't say, it all depends on which model you get in your hands..... although one things is for sure, the card is not made for the HTPC...... Since you have a Mid Tower Case it might squeeze itself in, but, the space is going to be too tight..... Don't risk it unless you're sure of what you're getting and the exact dimensions of it, plus, you have enough free space inside the case.
A HDD jutting out or the FP wire connector jutting upwards anything could mess it up. Especially since it's a Micro Board you'll also have a higher SB Heatsink.....
Better check it out directly....
And it's preferable not to post 2 threads of the same topic or content.....
http://www.tomshardware.com/forum/303953-33-which-smallest-hd6850-size-asus-6850
 
That's because no one knows what you're getting other than you....
What's the dimension of the card that you are getting?
If your case has that much space free without any hindrances then yes it'll fit.
If you have too much of clutter on the inside then even the smallest version of that card might not fit..
so it finally all depends on two things, amount of space in the case and the size of the card you're going to get....