82141 H/s max for r9 270?

[Rolf]

Looks about right to me

Im new to this. if I add another card will it be 82141x2? or the increase in speed doesnt work like that?

How many gpu card will i need to bruteforce a WPA of 10 hex characters (ABCDEF0123456789) in 1-2 days? atm it takes me 163 days, 3 hours with only 1 r9 270.

For brute force attacks, when there's enough workload (16^10 is perfectly fine), the speed scales nicely, so yeah, if you'll add another R9 270, you'll get twice the speed.

Basic math for the task:
16^10 / 82141x = 86400
x ≈ 155
So, you'll need 155 R9 270s to get the job done in a day, twice less for 48 hours.