How are you testing page load speeds currently ? If it’s real world users via Google Analytics reported page speed, remember it depends entire only end users mobile/desktop device and their ISP page speed too - i.e. slow mobile device with 3G mobile vs fast fibre internet on high end desktop.
You can test geographic page speed in more controlled manner via webpagetest.org. I wrote a guide on using it https://community.centminmod.com/threads/how-to-use-webpagetest-org-for-page-load-speed-testing.13859/.
If you’re looking at TTFB metrics that is also only one part of overall page load speed and is geographically dependent. This is due to Cloudflare not caching HTML content by default but only static files. So for optimal TTFB speed, you want your origin real web server to be hosted in a location closest to your majority traffic visitors and then put Cloudflare in front. For instance, my forums has 50% US visitors 40% Asian visitors and 10% Oceania. So my optimal geographic location for my origin is US West Coast as it sits in middle of US, Europe and Asian so equal round trip times for majority of visitors.
Cloudflare cache certain static content https://support.cloudflare.com/hc/en-us/articles/200172516-Which-file-extensions-does-CloudFlare-cache-for-static-content- but not dynamic/static generated html itself by default (which is what WPT TTFB is testing for). But you can tell Cloudflare to cache dynamic/static generated html content to some extent depending on Cloudflare plan you’re on via cache everything page rule but have to be careful to only do this for static html content and not dynamic html content (otherwise you would cache private logged in user content).
As to using Argo, make sure you’re looking at the proper page speed metrics to evaluate it’s effectiveness as Argo accelerates server response time which is only one part of overall page load speed factors. I did a write up of my Argo experience including page load speed metrics at https://community.centminmod.com/threads/cloudflare-argo-smart-routing-in-action.17517/ which can use to get an idea of what to look for when evaluating Argo and it’s benefits for you.
Hope that helps