I didn't find the list of maximum values on fansites, but I remember because I've actively participated in the test server.
The first changes that were made on the Bounty Ring, turning it into a Bounty Talisman (extra slot) also brought us the maximum values on test server, as Fluffey confirmed:

It started as 25% maximum on all effects and then only the bestiary had double percentage in comparison.
Then, he announced a double increase on all effects:

Confirmed all values:

So, the final max values are:
Damage: +50%
Life Leech (previously Reduced Damage): +50%
Loot: +50%
Double Bestiary Chance: +100%