Please someone make available the general index of altcoins vs. BTC how it's been doing in the time of carnage. (over the course of a few weeks, and also since the dropping through the latest floor)
I would say 10-20 largest altcoins would be good for the index, but I also heard indices with established methodologies exist.
You mean something like this:
http://coinmarketcap.com/currencies/views/filter-non-mineable-and-premined/But with a long-term chart of the top items?
I mean a table where there's a certain startpoint (for example Sept 15, when the BTC latest fall started in earnest). Then it lists how the altcoins have done during the decline. There's some talk in XMR threads that it has performed poorly, but some also say that it is better than most. A factual comparison would be really good obviously!

I'm collaborating with a domain expert subscriber to this forum, working to develop something that would seem to broadly satisfy the requirement, the project's working title is "SandRaiser", btw.
I've been engaged in backfilling the data, it needs a bit more work but I should have something for you to look at later today (TZ=BST).
There are three indexes at the moment and a couple in speculative development :
1. FullMonty/+ - all altcoins with a calculable marketcap (very rough and ready, obv)
2. Key30/+ - top 30 coins by marketcap
3. NonMinables - an index of PoS-only coins.
1 & 2 are presented with and without LTC, hence the "/+" and have been balanced at August 23.
3 is balanced separately about a week ago (can't recall offhand).
The arithmetic is based on the equations laid out in
S&P maths tech PDF docIs this the kind of thing you had in mind?
Oh, I'll chuck this in, as well - add a few facts to the mix, I posted it a few days ago in a separate thread, it may well have escaped your notice:

Cheers
Graham