Keyword domain with plural variation in the middle?

[NikNak]

Hi all

I was wondering what your thoughts are on keyword domains with a plural variation in the middle, I think that’s the best way to describe it anyway, for example if I wanted to target the term:

“fattest cat in America”

And I used the domain:

fattestcatsinAmerica.com

Would this still give me pretty much the same SEO benefit as adding an extra suffix character like:

fattestcatinAmericaz.com or fattestcatinAmericax.com or something similar.

Now I know this question is based on the assumption that keyword domains still work, so you will have to humour someone who is still finding they do, but assuming you still share my perspective would varying a singular to a plural right in the middle instead of using a suffix still be ok, one of the reasons I ask is because I just had a new site rank in the top 3 of Google doing exactly this and am wondering what other peoples experiences are?

One million thanks in advance

Nik Nak