Is it rude to stop in front of bikers stopped at a red light if you're generally slower, which will probably mean they will pass you again? What if you are generally faster so it saves you having to pass them?
Yes, it is rude to stop in front of another cyclist at a red light, especially if they are faster than you. That much is certain.
As Carey says, the best thing to do is to just come to a stop behind the already stopped riders. If you do decide to shoal, at least have the courtesy to be faster.
The number one rule is be considerate to other cyclists, motor vehicles and pedestrians.
Regardless of speed, it is inconsiderate to stop directly in front of a cyclist who is waiting for the lights to change, however there are different situations that could occur so saying to stop behind them is open to exceptions such as:
Whilst where you stop is important I think it is equally or more important to be aware of other cyclists (primarily in front and beside you) and not cut them off if you pass them. When you take off give any other cyclists plenty of room before you pull into single file. Cutting people off is probably the worst offence, especially as the first person at the lights will likely have the preferential line.