That dban recommendation as described = lost data, if he has some valuable data already thats kind of silly thing to erase it now...
He might transfer those files on the SSD, format it and transfer it back but for a wise person its no the best option and personally I never did such.
If he has only 1 partition it is indeed some kind of solution to get rid of old windows, program files... etc but you can do with with simple delete under which you have more control.
The migration to the new drive is almost a different topic and there is many ways that not include formating to do so, but it really depends what OP want to keep from the old drive if nothing then indeed format is a quick solution (not like you need a 3rd party software to do so, you can do it under windows)
Erasing boot sector is pointless, BIOS handles which drive to boot first so if reinstall OS correctly on the new drive (with old one unattached) after the final reboot you simply plug the old drive and set correct boot drive thats it. Its not like formating drive makes it to work faster again, reinstalling OS usually does (technically its not the drive working faster but the OS itself) but thats totally different story.
If OP really wants to enjoy a fast working OS then SSD is a real savior thus recommendations with SSD, especially EVO 850 are valid. Obviously you keep that Seagate (duh i hate them) as a secondary drive for storage purposes.
dreamer64 :
Doesn't windows re format so the same thing?
Yes it does thus i don't get what is so special about dban, its not like you need to fill HDD with zeros pattern to actually hide the files you have on the drive. (that might be confusing typical format doesn't actually delete the files from the drive it just clears the Master File Table thus drive "thinks" the space is empty there but actually you are overwriting the files which where located there)