There are a lot of important things discussed in that review like grain and resolution and overall tonality and "family resemblances," but film speed expressed as an EI is a fairly specific thing measured in terms of shadow detail. One question you can ask is "can I get a good picture by underexposing two or three stops in low light and increasing development to improve highlight and midtone separation?", and another question is "can I get an EI of 12800 with such and such a film?" Depending on your tastes, I would say "yes" to the first question, and in general "no" to the second.

There are no free lunches, and low-light is always going to involve some sort of compromise. Indeed, a bigger format means less DOF wide open. An SLR rather than a rangefinder or TLR will give you more mirror slap. Mirror lock reduces vibration, but why use an SLR with a normal lens if you're going to use mirror lock? Everything is sharper on a tripod, but a tripod can be an impediment to getting the shot. A longer exposure gives better tonality at the expense of camera and subject movement.

As a general rule, the increase in film area with 6x6 or larger over 35mm will beat the grain penalty that comes with having to use a faster film to compensate for slower lenses and less DOF.