While browsing the Circuit Studio documentation, I stumbled across this little gem on http://documentation.circuitstudio.com/display/CSTU/CircuitStudio+-+((FAQs)):
While there are no 'hard limits' per se, the software has been engineered to make it impractical for use with large designs. To this end, the PCB Editor will start to exibit performance degradation when editing designs containing 5000 pads, becoming virtually unusable with designs containing 50,000 pads. Degradation itself takes the form of progressive slow-down in PCB editing functions (such as routing, placing components, polygon pours, etc).
Now, I can't decide whether that's just a really awkward wording on their side or they have actually implemented some kind of "crippling algorithm" that kicks in after reaching 5000 pads and gradually inserts longer and longer delays, making your life harder and harder, trying to (not so subtly) nudge you towards Altium Designer? If so, wouldn't that be quite a weird thing to openly admit to just like that?
Even Altium struggles, if you have multiple large designs open. First it starts with "please wait a moment" window popping up several times, and then "chatastrophic failure". This is the time to save your work re-start it and close what you dont need. I think it has to do something with the memory used, but I cannot pinpoint it.
What I've experienced, with CS, that this happens much faster. At around 500MB used it start having this issues. So a few complex 3D model can set you back a lot.
Also, layer re-pour is exponentially growing with complexity. And online DRC can be a few seconds, which does not sound a lot, but if you have to wait 100 times...
This being said, you get some discount for AD if you have CS. If you dont know the tool, it might be better to learn the basics on that.