You would measure a faster performance - maybe 20%, but there would be absolutely no feeling of being faster.
I would recommend you simply add the new drive (which would appear as D: or possibly another letter). There are significant advantages in having a separate drive.
1. For backup. Having a second drive enables far faster and more secure backups then removeable media, although removable backups (at another location) of higly irreplaceable data is still needed.
2. For storing a 'drive image' of your current Windows drive which enables restore in minutes instead of days if your first drive fails, becomes corrupted or infected by malware.
3. Backing up a vital drive (the OS) drive which never gets large is far, far faster than one gigantic drive.
4.Having OS and data on separate drives can give a significantly faster feel because the two drives work independantly.