I recently did some testings about combat in Second Life. The viewer, as you can see, is a really complex beast of software and allows quite many tweakings to optimize the graphics settings for combat - and turns the view from pretty to really unrealistic. But this unrealistic few gives the fighters, who are using it, quite some advantages. Even more so, you are not able to detect it if someone uses that kind of view.
The first video shows a normal view, graphics settings to "high", on the sim named Ivalo from the ship to the city gates. It is quite a beautiful sim, with a big forest and nice surroundings, as you can see for yourself:
Beautiful, isn't it? The second video shows the same way, but all graphics settings set to low, range is still 128m, but the rending of alpha textures and other stuff is also turned off. That's the kind of setting which many fighters in Second Life prefer to squeeze more frames per seconds out of their client. As you can see, it is quite different, and even more important, since all trees are almost turned off that way, you are able to see the city walls and the outlook post, giving you an unfair advantage.
But since you cannot enforce normal graphics settings in Second Life per se, that's what you must take into account - someone using that kind of settings.