I'm not aware of research. It's well-known of course that caffeine helps, and many people think that the taurine in energy beverages, either alone or in some connection to the caffeine, also helps. If you're going to be relying in part or in full on caffeine, try to stay away from it at times when you're not using it for attacks. As with so many other things, it seems you can build a tolerance to caffeine that reduces its effectiveness. Depending on which Monster drink you used, you might well find that it has less caffeine than the much smaller, quicker-to-get-down energy shots, such as 5-Hour Energy. A "standard" Monster has about 80ish mg of caffeine, whereas the standard 5-Hour Energy has more than 200mg, and the extra strength 5-Hour has close to 250mg.
Assuming that O2 has worked for you but isn't now -- some/many people find that if the pressure in the oxygen tank is low (maybe 1/3 full, or less full), O2 doesn't work as well.