There are good reasons why most manufacturers won't certify their regulators for use in greater than EAN40 or so, largely the same reasons that your gas supplier won't offer bottled oxygen at greater than 2400 psi pressures. Given enough pressure and enough oxygen, the tiniest bit of fuel is highly dangerous. Given enough pressure and enough oxygen, pretty much everything is fuel.
The first stage seat in any regulator is a scary place: high pressure, high velocity, repeated flow restriction, flammable materials. Now add high oxygen content to that mix and you have a very serious problem. The biggest hurdle to making a regulator oxygen safe is the materials used inside the first stage. Steel, aluminum and titanium can all be removed and replaced with brass and nickel but what do you do with the soft bits? You can swap Buna for Viton or EPDM but both of those materials will burn, given enough pressure and enough oxygen. Probably the toughest issue is the high pressure seat, a toasty little bit of plastic that sits exactly at the worst place you would want something flammable - there is only so much you can do to engineer the flow path to minimize frictional, adiabatic and impingement ignition problems and the materials issue is almost insurmountable. Nobody has found a resolution for the high pressure seat issue. Yet.
HOG has done a good job (far better than most) minimizing the dangers of use in oxygen but the laws of physics still apply. Given that that it isn't possible to reduce the combustion risk to zero, any manufacturers decision to certify for oxygen use becomes a risk/reward evaluation. As scary as the inside of the first stage is, there is another place that is even more frightening: the inside of a courtroom. The laws of physics maybe inflexible but the laws of man are often whimsical - and vindictive. A little bit of prudence not only seems reasonable but necessary.
So how often are you actually going to need a regulator that can handle higher than 2400psi of pure oxygen? If a 40cf bottle at 2400psi won't hold enough O2 for your plan, is higher pressure a better solution than a bigger bottle? Remember, you won't be using this bottle below 1.6ATA, if an 80cf bottle won't hold enough gas, you're doing some very long hangs or breathing like a pig.
) I suppose sometimes when I post in the manufacturers forum, I am looking for them to respond. That would be my view in how posting here would be different from the same post in the Regulators forum... 
