I have owned several ST-70's and have heard several ST-40's. The 70's extra watts help in the bass region. Have also heard an HF-81 over several years. Never was that impressed with it.
There are some great ST-70 mod sites; here's my favorite:
http://www.tronola.com/html/st-70_mods.html
There are some great ST-70 mod sites; here's my favorite:
http://www.tronola.com/html/st-70_mods.html