The five slot board with Linux is fine if you're okay with risers, DIY mounts, and creative cooling solutions. It's a personal preference of couse, but I prefer self contained rigs that can be mounted with stock components and without too much fiddling - which helps maintain their re-sale value too. :-)

Seriously, calm down. Markets are about as stable as anti-matter these days, but they have always trended upwards and unless you have reason to think they won't, they'll continue to do so. Justr because the fall from $30 to $20 feels like more than a fall from $1.00 to $0.66, doesn't mean it's not exactly the same. This has happened many times now: you'll just make the daytraders richer if you 'cut your losses' IMHO.

A denial of service attack costs money and resources (infected PCs valued at $0.25 to $3 each depending on country and bandwidth available).
It's a service that has a tangible real world value.

So it's either someone very bored who has access to his own botnet, or someone is actually paying thousands of dollars per hour just to annoy miners.

There isn't really any financial gain here, since difficulty level only changes every 2016 blocks.
Attackers chances of finding blocks does not go up simply because he forces other miners out for a few hours.