Now this is a hard question, I have both and hunt the same areas and the deeper silver come in about the same depth with either machine.
If I go with the air testing I have done with coins the F75 comes in the clear winner. But the compare test between the 2 machines is not what I would call apples to apples, the coils are not the same size or type.
The deeper silver I have found in my area is about 5" to 7" and my brother has test garden with coins up to 8" and both machines with stock 8" and 11"DD will hit the 8" coins in the test garden.
I would like to say one is over the other, but for me in my area they both hit just about the same in the ground.
I posted this little story the other day so you may have read this. I was hunting a couple of weeks ago and found a nice half $ with the F75, and of course any time I find something like that I really pound that area thinking maybe more, but this time nothing. A couple of days later I was back with the 1270 so I thought I would check the area where I found the half. Within 2 feet of the half dollar hole I got pretty solid hit and out came a nickel and a silver dime.
I hunted with the F75 first and got the half, but I can say this without any doubt if I would have been there with the 1270 first I would have got the half and the dime. So with that said the 1270 may have the edge.
Both pretty good machines.
Ron in WV