should I go back to win7 - t420?

I've been using win 8 on my t420 ever since it came out. I had no problems with it, but sometimes I feel I should go back to win 7 for better driver compatibility (maybe?).

I cleaned the hardware, replaced thermal paste, but still get slow downs, specially with firefox.

Should I just go back to win 7 and maybe wait for win 10 RTM mid 2015?

 

I don't have a proper answer for you since I've never used W8.x on a T420. Hardware-wise, I see absolutely zero reason why a machine from this era should have any issues running it.

If you're happy with W8 apart from the slowdown issues, try troubleshooting where these could possibly be coming from.

Personally, I see next to no point in running W8 in a non-touch environment but that's me.

Save an image of your current W8 install and re-install W7 if you're so inclined. Compare mental notes with yourself and proceed accordingly.

Good luck.

 

That's a good idea! It will save you the hassle of reinstalling it should you choose to give it another shot after installing Windows 7 (you can also create a separate image of your Windows 7 install).