All the detectors that you mention are capable of going really deep under the right conditions. For example my GT has picked up targets at 6 inches while working a beach cut of two feet, So I think I can say with certainty that my GT will pick up targets at least 30 inches deep.
The list of things that will effect how much depth you might experience is long. In Your quest for deep you might consider some of the following
The size of your coil. A really big and heavy coil will slow you down so that you will probably get deeper.
Whether you are hunting in all metal. and your targets are all metal.
Your threshold setting (If you set it to high you will not hear any tunes) .
What you are Discing out. (If you disc out deep targets you will not get any).
The type of soil you are detecting. It is difficult to go deep thru granite.
The moisture in your soil. If the water is deep it is hard to swim and go deep at the same time.
The mineralization in your soil. In Iron Mountain Michigan it is really difficult to go deep.
The trash in your soil. A six inch layer of pull-tabs makes it really hard to get deep.
Do you normally hunt with your coil scraping the dirt ? The more dirt you scrape away the deeper you will detect.
Do you get a good nights sleep before you go detecting for deep targets?. (Deep sleep makes you more alert to deep targets)
Do you normally follow a hunter who is finding all deep targets ? (this will make it difficult for you to pick up deep targets)
To answer your question - can they all go as deep on the same target? They probably can but will they?
In reviewing my list it is obvious to me that going really deep has little to do with any one detector.
It has a lot to do with personal attitude. Always think deep and sometimes you get lucky..
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