I'm not aware of any rule of thumb numbers (like x points = y hp/tq), but generally, increasing the compression ratio will boost low-end torque and extend the top-end power range

 

Higher compression within reason can also increase cruising mileage too

I ran 11.3:1 in my 418 and cruising on the highway it would get around 16 which was close to what the stock 5.3 got, now get it in the city thats where the single digits came on quick

 

I've got an LQ4 and I want to mill my 317's down .040. Will I need a shorter pushrod?

 

Yes sir you will, I don't believe that the lifters would like that much pre-load, if they could even make up that much. I'm guessing that a 7.35 pushrod would work, but you really need to get a pushrod length checker and do it right