I have found that if I sort peers by B/s In and change the bandwidth priority of all peers with at least 1 KB to High Priority that generally their speed increases. Sometimes the increase is phenomenal and will go to MBs. If I change the bandwidth priority of peers with at least 1 MB to Ultra High their speed can more than double. The time left to complete the download can drop from days to just a few hours. It would be nice if Tixati could perform this way by default.

Hi,
The priority for torrents or peers  doesn't increase the total download/seed speed of Tixati or any torrents client , it's just there to take speed from a torrent with low priority and give it to the one with higher priority. The same happen to peers connected to the same torrent, by the way changing peers priority is an abusive act, imagine yourself downloading and the seeder give you low priority, while he choose high priority for other peers.

The idea that altering bw allocation is an "abusive act" is not founded on reality. Study "tit for tat" game theory.
It is actually built into the bit torrent protocol.
see:
 https://en.wikipedia.org/wiki/Tit_for_tat#Peer-to-peer_file_sharing

Requesting huge download speeds while severely limiting your upload speed, especially with the same user, is repugnant, ugly and yes abusive.

When reciprocity is used as a reward, it is a positive thing. Both the seed and the user should feel good when respect is shown.

Respect
Mutual aid
Reciprocity
Sharing

All things that build community

Yeah of course i know about that, but changing peers priority manually will not help the "tit for tat", that's why uTorrent and some other famous torrent clients doesn't have that option although they all manage the "tit for tat" like Tixati.
If you want to make sure everyone seed to you almost as you do, you can just go to Bandwidth > Advanced > Outgoing Seeding/Trading% , The higher percentage you choose for Trading , the more "tit for tat" will be taken in consideration by the program.
Changing Peer priority can still be helpful in some situations, like when you are downloading a torrent that has only 1 seeder and 1 leecher, you can here give higher priority to the seeder to get the most from him before he close his client.