Thanks, Original Ralph, for your suggestion. Originally, I tried migrating from HDD to SSD via Samsung Magician software, but this apparently caused a problem with alignment (as indicated by AS Benchmark software). Since Win7Pro cannot be installed directly to the SSD (BIOS/UEFI sees the drive, but Windows Installer does not -- and also tried running install from Windows (rather than booting to the DVD), which I thought was going to work... but didn't), I took your suggestion of migrating from another SSD (e.g., SATA) to the M.2 SSD, but instead did it this way:
I cleaned the HDD (remove all partitions and format as NTFS at 4096 byte allocation unit size), and I did the same to the M.2 SSD, but also did a secure erase via DISKPART (clean all) beforehand.
Then, I migrated (this time I used Macrium Reflect instead of Samsung Magician). Everything seems fine: running well, boots to Win7Pro, AS Benchmark says alignment is okay, and this is confirmed under msinfo32, so I am happy!
Thanks for your help! Hope this info helps anyone else with similar issues.