The speed of the cloned OS it self remains, since you are carrying over everything incl. viruses, etc.
The overall speed depend also by the speed of the target clone HDD/SSD.
Transfering normal datas to other HDD is easy, just do normal copy.
If you want to avoid issues, keep the target clone HDD/SSD empty, do not put anything there beside the clone from source HDD/SSD.
Just copy your datas e.g. music, photos, videos, etc. to other HDD first. Delete those from the source HDD/SSD before cloning to simplify the clone process.