Mixed hardware questions - 1080Ti's and 2080

We currently have a password rig with two 1080 Ti's and we are looking to add 2 more GPU's.  We are trying to decide between the 2080's and 2080 Ti's.  We are currently leaning towards the 2080's but had some concerns about running different video cards especially since the 1080Ti's have 11 GB of ram and the 2080's have 8GB.  

I know people run different hardware all the time but I'm curious if there is some sort of performance implication.

Mixing hardware is fine.
While mixing hardware won't cause any serious issues, when starting an attack that requires a large amount of VRAM, if mixed cards are used, you will be limited by the memory of the smallest card in use, which may hinder some attacks a little bit. 8gb is still a fairly decent amount, this really starts to cause problems when people try to mix in smaller cards with 3-4gb of VRAM alongside cards with 8-12gb of VRAM, especially after setting up and getting used to attacks on the larger cards.