In the stargate saga in many occasions they transmit EM though the stargate. In particular in ST-A in S01E17 "Letters from Pegasus" they get to transmit a burst of data within 1.3 seconds. What would be the bandwidth that stargate can support for EM transmission?
It isn't exactly clear how stargates operate. They aren't simple wormholes in the classic scifi sense. Light doesn't pass through them. For example, if you look at the event horizon of an activate stargate you can't "see" through to the other side. My assumption is that they deconstruct matter which passes through their event horizon and then transmit the configuration of the object as information to another stargate which reconstructs the object at the other end. This probably means digital information.
The question of "how much bandwidth" probably relates to the surface area of the event horizon, assuming that an unbounded amount of matter can be passed into the stargate and transmitted as a stream. The "bandiwdth", then, is probably something like the total amount of information density available at some small length (let's assume planck length) spread over the surface area of the event horizon. This number would be astronomically high as it is clearly modeling state down to the atomic level... and maybe smaller. If you really want to do the math, I guess you could try to calculate how many bits would be required to model a homogeneous slice of neutronium (high density matter) with a surface area equal to that of a stargate. This assumes stargates can transmit neutronium. If you don't think they can, pick something with lower density.
In calculating the bandwidth, one has to also consider compression algorithms. Because of our ignorance with respect to what algorithms might be employed, I don't think we can calculate how much bandwidth the stargate actually provides. We can only calculate the upper bound of how much it could possibly need (as I described above).
It's high enough not only to transport dense matter (humanoid replicators which are hinted at containing Neutronium, can), but also data transmissions of beam transporters, which was essential for Morgan Le Fay's precautions to safekeep Merlin. I don't know whether it also works with rings or Asgard transporter beams.