Artifactory's REST API does not limit the size of artifact uploads; however, you do need to be aware that it is possible for your connection to the database to timeout during large file uploads.
For an on-prem installation, if you wish to upload large sized artifacts please make sure that you increase the connection timeout for your database. You will need to consult the documentation for your particular database to determine how to do this.
If you are using Artifactory as a SaaS service in the cloud, you cannot modify the database configuration, so you need to reduce the size of artifacts you upload.
Uploading a large file should not cause any performance degradation in artifactory directly, although as with any data-movement, it will have some impact on your network's bandwidth.