Why is DayZ running worse on my new hard drive than on my old one?

So the stock harddrive on my Lenovo G505s laptop recently crapped out, so I bought an average priced SSHD (I was tight on money, couldn't get SSD) and clean installed Windows 7 OEM (the laptop previously had Windows 8). I didn't transfer, just installed all of my old games, including DayZ.

Now on my old HDD, I was able to run DayZ comfortably on average settings (messing with config settings, I got about 40 fps in cities, 60 outside). I figured with this new SSHD, plus having W7, would let me run it at least a tiny bit better, it gave me a boost for my other games. But for DayZ it make it much worse.

Now I have to reduce the resolution, make the config settings for view distance lower, set EVERYTHING to low in-game… And that get's me about ~25fps in cities, 30-40 outside! Now I can live with the fps drop to a degree, but now my game looks terrible.

Just wondering what the hell happened. I know DayZ has terrible compatibility issues. Does it have to do with the SSHD? Windows 7? I can't imagine it running better on W8 that W7.

All drivers are updated properly, also.

Added (1). I mean, if anything, it should run exactly the same as when it was on my old HDD. And btw, the new SSHD is a Seagate 1TB (ST1000LM014). Everything about is better than the stock harddrive.

If the hard drive is the only thing you replaced… Have you reinstalled your video card driver(s)? This is assuming you had a video card to begin with.

Windows 8[.1] is slightly better than Windows 7 at running games. You have got a 1Tb SSHD so you could dual boot Windows 8.1 and 7 while partitioning another drive for the Steam directory. DayZ should be getting a renderer update soon anyway so if you don't want to get Windows 8.1 you can wait. Another thing that might have happened is you installed a 32-bit version of Windows 7 but it's unlikely. There are videos comparing Windows versions and their fps on YouTube