With the introduction of Hodgdon's Retumbo powder, I saw new potential advantages for this overbore wildcat. That is, nearly a full case with a stable powder. Previous tests with H870 showed unacceptable velocity variation.
This past summer I rebarreled my M70 action with a 32" PAC-NOR stainless steel match barrel 1 in 9" twist with Sendero contour and put it all in a "skim" bedded Choate Plaster stock. It was topped off with a Burris 8-32x Black Diamond scope. The whole set up with scope weighs a touch over 15lbs. The following data was collected with a Beta Chrony and Peak strain meter.

bullet Charge vel pressure
95 Horn vmax 88gr 4150 67000psi
108 Lapua Sce 83gr 3990 68000psi
120 Nos BT 80gr 3810 67000psi
120 Lost riv 75gr 3715 64000psi
140 Hor Amax 70gr 3450 65000psi

The 95gr Hornady Vmax vaporized at about 50ft down range. My shooting buddy saw a puff of smoke! The added barrel length contributes about 40-50fps/inch over the 28"barrel previously tested.
I settled on the 108 Lapus Scenar(BC=.478) 82gr with velocity around 3930fps. Typically get .25MOA-.5MOA at 200yards. This set up just doesn't like the heavier/longer bullets. There is still trouble with fouling. I get 7 shots in the group from a clean barrel (wipe out clean)then it starts throwing fliers. Most likely a use for such a rifle would be a long range deer and varmint rifle.

Do you feel the extra case capacity of your wildcat will get you much advantage over the .264 Winchester in the 6.5mm bore size ?

My 24 inch barrel .264 will drive 100 gr bullets to 3600 fps and 120 gr to 3400 fps . It looks like give it 8 more inches of barrel and it would nipp right at the heels of your larger case .

You mention a Peak strain meter . Who makes it , where did you purchase it
, and after using it , what do you think of it ?

Because of the increased powder charge I think the longer barrel gives a greater return in this cartridge. When loading to the same pressures, my 6.5 WSM (which closely parallels the .264 win mag) is about 150-250 fps behind the STW.
The peak strain meter is made by fabrique scientific, costs $150 for the unit, and each gauge is $14. Having used this device, I wouldn't feel comfortable loading wildcats without it. When I first bought it I tested several of my rifles and they were all over pressure 70-75K psi. These were all worked up using traditional pressure signs. eg. case sticking, primer appearance, ejector marks on case. The problem is that as soon as one of these signs becomes apparent, you are already over pressure significantly. Unfortunately, using reloading data is still no guarantee that your within acceptable limits as I have seen dramatic differences between rifles with the same chamber reamer and gunsmith.