Is latency and pocket loss the same between different Tiers

Hi,

My questions is mainly about Essential vs. Preferred Internet plan. I do not need high bandwidth rates as I do not do any extreme internet stuff. But I do use my connection for pretty basic VOIP needs. My question is,

Is there a difference in Pocket Loss and Latency performance between Cox Essential and Cox Preferred Internet only plans?

I use SB6121 modem as I read some good reviews about it, but it is a bit older than something like SB6180 or SB6181.  Is SB6121 is a pretty solid modem for what I need or should I look into upgrading (once again, I am not looking to speeds above 50mbps/5mbps as downloads and 4K videos are not in the span of my interest for at least a next year or two).

Thanks,