Just to throw this out there - SSDs really shine in small, random writes and reads. It has to deal with the way the NAND Flash memory reads and write to individual pages and blocks. SSD's are great for OS's and applications.
1) SSDs are not the best storage medium when it comes to transferring large files (such as 8Gb). Standard mechanical HD's still hold a large lead in this one task. It has to do with the fact that a SSD cannot write and erase individual pages at a time. I tmust do entire blocks, saving the block's contents to its cache, erasing the block, and re-writing it. That takes time. So you shouldn't be surprised that it taking so long to transfer such a large file.
2) With a little less than 50% left on the hard drive, you could be experiencing some degradation. I'd suggest you secure erase the drive, try upgrading it's firmware and have another go at it. Of course back up all your data. If you want, you could just make a drive image to help save you some time.
