Upload & Sell: On
High ISO when it's in daylight is a bit different than high ISO at night, from what I've seen. The grain is more notable in night photos.
That and yes, at a certain point you're going to lose a lot of DR and the photo will be usable for news, but not for a portfolio (I'd say my usable images would be up to 12.8k ISO, and cutoff for acceptable DR + editing at 25.6k/51.2k). Past the 12.8k ISO mark, I don't push my D4 to unless I really really must (which hasn't happened yet).
Side note: will upload a bunch of 10k+ photos tonight or tomorrow. Shot 3 back-to-back-to-back school productions last week from behind orchestra section.