Lightroom does not have a Limit for the number of Pictures we can keep in a catalog
It all depends upon the Computer hardware whether it can handle it or not.
Please make sure your computer meets recommended Requirements as suggested in this link(Refer System requirements
You can always Optimize your catalog to improve Performance (Refer Optimize performance) and How to Optimize Lightroom 5 | The Complete Picture with Julieanne Kost | Adobe TV
Still if you if you feel like Lightroom is slowing down, You can Create a new catalog
Let us know if that helps
I have almost 300.000 photo's in my catalog, should I divide this?
Don't do it. You haven't given us a single reason to split your catalog, and in virtually every case I have seen, there is no reason at all to split your catalog. Splitting your catalog has many more drawbacks than advantages (which again, you haven't mentioned even a single one)
I have a Big Mac
3,4 GHz Intel Core i7
32 GB 1600 MHz DDR3
NVIDIA GeForce GTX 680MX 2048 MB
This should do it, right?
I heard about a 100.000 pics limit for one catalog.
I have CC now, and started of on face-recognition, thát seems to slow LR down a lot.
Wherever you heard it, that 100000 is just plucked out of the air.
Processes such as face recognition slow Lr, so switch it off if you don't need it. Splitting your catalogue will just fragment control of your pictures and workflow.