I am primarily civil war relic hunter in Mississippi and search for coins when I can't make the long drive to my hunting spots. I have an AT Pro and have enjoyed success w/ it. I am looking for a backup/upgrade machine and looking hard at the F70 or F75. Is there a big drop off from the 75 to the 70 as far as performance is concerned? Financially, I can get the 70 but would be stretching it w/ the 75..Again, I am looking at this from a relic hunting point of view..Thanks for the help!