There are so many variables between detectors; ie.... process speed, 'stacked' filters, resonance, coil config, operating freq, Sensitivity vs. white noise.... etc.....
The (current) ideal field intensity footprint for small low-conductors is a "elliptical" ""DD"". The intensity of the field-strength is very dense within a electromagnetically confined corridor, thus placing a higher level of energy into/on small objects....even over 'round' DD's. Concentric coils have the electromagnetic energy much more dispersed (thinned out); hence less detection of small objects; yet, inversely & inherently more stable over E-DD's.
Comparing the 36-X2 to a 1270 is somewhere between apples-to-apples...and...apples-to-oranges. Comparing T-2 to F-75 is apples-to-oranges when F-75 Jewelry mode is invoked, higher sensitivity settings,,, '0' zero discrimination....and small jewelry is being tested. Comparing F-75 to 1270/1236-X2 is comparing apple-to-school bus. Take that true 10K (NOT gold plated), thin-band, Size '3' kids gold ring.....and use a pair of side cutters and 'cut open' the ring. Keep it in a circle.... but keep the cut 'open' so as to break continuity of circle. This will (forever) be your current & future test-standard by way of ALL future comparison head-to-head testing. ((( You may already have some form of a low-conductor "test-standard" ))). You will learn that 1236 & 1270 will not detect this target. The T-2 may detect it to approx 1".... assuming maxed out settings. The F-75 will detect it to approx 3". A Gold Bug-II will get it at 4".
For the type of hunting you are doing, I would recommend a GB-II with "Iron Disc" switch invoked..... assuming mineralization is not severe. Then calibrate your learning curve to sweep-speed vs. distance-covered "Target Size Profiling"..... and recover the targets that meet your size criteria.
The F-75 would also be a good choice utilizing stock coil config.... or future smaller elliptical DD coil. And the F-75 is also a General Purpose unit.... should you decide to dabble into other types of hunting arena.
Keep in mind..... if you hunt in bad ground; good targets may ALL want to report as iron.
Concentric coils like circumferentially 'round' objects; .... E-DD coils hardly care.
A standard concentric coil on the T-2 or F-75 would most likely make the unit less 'chattery' .... as it would then become 'less' sensitive to all of the tiny trash this Earth conceals. A concentric coil would also 'desensitize' the unit to tiny objects..... but amp-gain coin-sized objects,,,,...... especially at depth....possibly (most probably) trumping all other detectors for overall total depth. A concentric coil (vs. DD) in bad ground,,,,,...... well, you can't win them all!
Tom