Should I use the old "knowledge-api" or migrate my code to the new "kie-api" on BRMS / BPM Suite 6 platform ?

Issue

• I want to migrate from BRMS 5 to 6 in order to get better performance. Should I use the old knowledge-api or migrate my code to the new kie-api ?
• Is there any difference between knowledge-api and kie-api in terms of functionality and performance ?
• Can I use the new PHREAK algorithm in BRMS 6 to get better performance with the old knowledge-api ?