What are effective (cache?) settings for reducing disk I/O?

[naugas]

When running utorrent from my small usb external disk, I constantly got a lot of disk overload 100% even at rather low speeds, and downloads stalled. When I fiddled around with the cache settings, and amongst other things changed the cache settings to 256 MB, it started to work much better. It was something else than the cache size that made the biggest difference though, but I don't remember what it was. I don't remember anything about what I changed really, I just tried one thing after another, but it sort of worked. When the download is reaching 2-4 MB/s though, I still get disk overload. When just copying and writing files, speed is 8-12 MB/s. Network speed is potentially even faster than that.

Probably my settings are far from optimal... Does anyone have some suggestions for good settings of the cache in a situation like mine? At least a starting point, and tips for what variables to change and what they do. I can't find any "official" recommended tweaks, which really surprise me, as the default settings were almost unusable.

Screen shot of my current cache settings:

edit:

I did also reduce number of connections and connected peers per torrent, 200 connections globally and 40 per torrent are my settings now. I usually have 1-5 downloads at once, depending on speed. Only one download if it by itself can reach speeds to cause disk overload, more downloads if speeds are lower.

[Firon]

Enable write out finished pieces immediately.