The 250 will already be faster. Make it your new boot drive. Use it for System, Applications, and Paging files.
Think about things you may do that would fight over the disk drive, and move some of those to the second drive.
Do not be tempted by the siren-song of creating a Striped RAID out of two SSD drives. It adds enormous complexity, precludes having a Recovery partition, and crates a very fragile drive that, if anything fails, ALL the data on both drives become unsalvageable.
Since that comes up as an issue, you also need to have a Trusted Backup. Do you? How current is it? If you lose your drive during the changeover, will you lose everything?