After upgrading to 4.2.2 my site seems a lot slower. Is this common behaviour?
Already turned off the automatic cache rebuild option.
Especially the product listings pages and productdetails. Admin area is slower too.
Who knows where I should start looking?
Did you make any other changes around the same time, or just the upgrade alone?
Nope, just the upgrade.
It seems you’re not the only one who observed this. After upgrading to CS-Cart 4.2.2, the site is moving much slower with no other themes or add ons installed. I’m talking about the default Responsive theme which comes with CS-Cart and the default CS-Cart add ons.
The biggest problem is that if the default Responsive theme is moving much slower, especially on mobiles, then this will directly affect further store customizations and all of the theme and add-on developers, and then the end users.
On the other hand, your server optimization and speed becomes more important than before, because you definitely need more resources especially if you upgraded your CS-Cart and used a non-responsive theme before.
CS-Cart developers need to escalate “site speed” to the top of their “to-do” list.
How come you CS-Cart guys don't market your 'own' server that's optimised for your cart ? Not those third party ones that people complain about but your own server.
They are working on it. 
We have a dedicated server and CS 4.2.? is VERY SLOW if you try to use one of the out of the box responsive themes/skins.
Just using the standard skin, not responsive.