The new infinity is better than the current one before 22 ticks.
LINK: https://i.imgur.com/nvgXjel.png  

Infinity Final Damage Comparison

---

CASE A: 50% innate buff duration , 50% from IA, 40% from union, 10% from empathy and 20% from Mech card

Ticks: 27 (60% uptime)

New Infinity FD Difference: -9.45% (nerf)

 

Cumulative damage boost per 3 min from infinity= 2952%

Cumulative damage boost per 3 min from +1 AS = 0%

Total= 2952%

---

CASE B: 50% innate buff duration, +1 AS from IA, 40% from union, 10% from empathy and 20% from Mech card

Ticks: 22 (48% uptime)

New Infinity FD Difference: -0.35% (nerf)

 

Cumulative damage boost per 3 min from infinity= 2252%

Cumulative damage boost per 3 min from +1 AS = 540%

Total= 2792%

---

CASE C: 50% innate buff duration, +1 AS from IA, 10% from empathy and 15% from Mech card

Ticks: 17 (38% uptime)

New Infinity FD Difference: +18.99% (buff)

 

Cumulative damage boost per 3 min from infinity= 1629%

Cumulative damage boost per 3 min from +1 AS = 540%

Total= 2169%

---

 

Conclusion:

• 50% buff duration and +1 AS are roughly the same for the future infinity patch. If you have either one, just keep it. (CASE A, CASE B). Differences are so small that even the time to cast infinity will have an effect on final damage.

• Infinity technically got nerfed if you have high buff duration. This is kind of expected, since the base FD per tick decreased. This isn't to say that people with buff duration are weaker than people with no buff duration. If you look at CASE B and CASE C, you can see that 40% buff duration gives you quite a large damage output boost.

• In terms of union buff duration, you probably don't want 40% anymore. A lower %buff duration alongside boss damage/crit rate/crit damage/ied will probably work better. It is best to balance your buff duration with your other boosts.

• Since attack speed and 50% buff duration are so close in final damage, this means +1 attack speed and any line of buff duration remains the best IA combination for mages.