How do i get the "purest" search results (e.g. every personalization incl geographic turned OFF)

I want my Google SERPs to be as "pure" as possible, with every personalization / historical search weighting thing turned off (aka free from anything that might skew them so I can do apples-to-apples comparisons to track performance.) So what I do before I run a SERP audit is:
(1) I make sure I'm signed OUT of Google
(2) I clear my browser (Chrome) cache and all cookies
(3) I go here: google.com/history/optout to DISABLE customizations based on search activity.

HOWEVER, there is still SOME personalization going on, AT LEAST GEOGRAPHICALLY, because even after I do the above 3 things, the SERPs are different (in some cases dramatically) depending on where I'm searching from. For example, when I run a search for club promoter when I'm in Miami, there are a lot of Miami-based nightclub-related pages in my SERPs. But when I run it from Montreal, there are a lot of Montreal-oriented pages. And the difference can be DRAMATIC in some cases: when I follow the 3 steps above to turn off all personalization, and I run a Google search for keyword XYZ:
(i) when I'm in Montreal, my website is #56 in Google SERPs
(ii) when I'm in Miami, my website is not in the top 500 (!!)

So two questions:
(1) Is there anything else I can do to make my search results as "pure" as possible? (esp. related to geography?)
(2) What could account for such a DRAMATIC difference (described in (ii) above where my site can move around hundreds of slots for the same keyword search from different cities)?
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