If total bike then componentry: at least 105 (and maybe preferrable due to possible breakage). Even XT is nice on a 'cross bike. Especially focus on wheels. I need handbuilt and quality rims.
If total bike then tires. What are you paying for? You need a good pair of tires.
I also like a carbon seatpost.
I prefer V-brakes, discs are always nice. If I walked into a shop and they had a cross bike with cantis I'd probably ask them to swap Vs in even if it cost me.
And the most important thing is fit. Does it feel nimble but powerful?!?! Weight is important, but you can be riding a feather and it won't be fast if you're uncomfortable and it's handling is sluggish.
Best question to answer is: do you feel fast on it?