Well, I can't see my TV's screen when sitting in front of the computer and vice versa, so having them display the same thing is actually what I need. And as for SLI, the most graphic-intensive software I use is Windows, so I don't really need a lot of horse power (hence the cheap cards).
Coming to think of it now, if both cards show the same thing, I might have resolution issues, as my TV has a much lower resolution than my monitor. But I can make do with having to lower the resolution when watching TV, so that won't be such big an issue.