Would it be possible to add options to
a) cache more received data before it's written to disk
and
b) allocate more memory to cache data being uploaded
?

I find that KTorrent's constant disk usage can be distractingly noisy, and worry that the heavy access may be wearing the drive out unnecessarily.

I also think grouping 1MB or so of the pieces before writing them to disk might be a good compromise between memory usage and frequency of i/o operations. With the current method of writing pieces out as they are recieved, KTorrent makes my computer iowait a lot when downloading quickly.

KTorrent shouldnæt be trying to emulate the OS. If you find that your OS doesn't cache enough, tune that instead (using sysctls and whatnot).

For example uTorrent have ability to cache reads and writes for faster perfomance. Maybe it's because of not very good caching in Windows, but I think it's because cache settings for torrent-client not so good for everything else.

Like what was said above, the OS should already do a good job at caching disk reads (even Windows, but perhaps not with default settings). There may be some advantage to application-level write caching though. For torrents it may be desirable to maintain large buffers and wait before writing out data; any data lost in case of a power failure can just be downloaded again.