My HDD can't keep up and I have 30 GB of free RAM, Tixati only uses 300-400 MB of RAM at most. I have found many threads around the internet with people asking for an option to increase the write cache but without a real answer. Many persons have 100-1000 Mbit/s internet connectivity today and mechanical hard drives have a hard time keeping up with that, especially since torrent writes chunks in random positions during a download.

Other than this I'm happy user of Tixati, it feels stupid that I can't use the full bandwidth I am paying for due to a caching issue.

Using windows x64 I see Tixati max out at 30GB ram (64GB intalled).

just turn off windows write cache flushing for selected hdd, unless you are afraid of power outages, it will work much better than anything client would implement

i suggest in addition to above:
1) place whole torrents folder on different drive,
2) place downloading and completed folders on different drives (modern (nt60) ntfs driver allocates files without fragments if it knows file size, so "move on complete" should eliminate all fragmnts)
3) dont use sparse files
4) use separate partition for program folder (with core2.dat and incmomplete-pieces)
5) disable last time access stamp (see HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem windows registry key)
6) make sure that $MFT in in one piece and not fragmented, clean it from old not existing files
7) use some defragmentation software with ability to prevent fragmentation
8) use server operating system