The real "GFWaaS" is when you intentionally put blocked keywords on a HTTP page, triggering GFW to reset user connection. That way you can block Chinese users from accessing your website. And it's free.
My suggestion is, may be add more web browsers to your service, make it a browser compatibility test platform, and (innocently) put few servers in China. People will figure out what's going on themselves :P
But the keyword is not hard to find, really ;P
"Tiananmen square massacre"
"Free Tibet"
"Falun gong organ harvesting"
"Winnie the Pooh"
That's China /shrug
It's also highly dependant on the time of day. Foreign sites are near unusable from around 7pm onwards
The reason your site 'slows down' may be that your site is blocked, or the embedded Javascript (such as Google Analytics, Adsense, DISQUS) or CSS/Web Font (such as Google fonts) has listed on GFW's blacklist. I feel sorry that my last reply may be not made it clear, I mean that the point of this project is not all the truth (why your site is slow), or even a little misleading. Since running website for several years, I must be honest point out that if the mainland China market make sense to you and you want to keep your website always smooth, the only way is to place the server in mainland China or Japan, all other testing, optimization is a waste of time and money.
If I do a git push to gitlab then it can take 90 seconds to even start responding.
I hate the internet so much here that I'm never returning until the firewall is taken down. Some nights I just give up and go to bed early