Truthfully, the answer is this; you’re going fast enough when you actually retain the information you are studying. I know we’re all (including myself) tempted to rush things sometimes. This is especially true when you’re not seeing any immediate progress (or at least, you’re not perceiving it as such).
But, when it comes down to it, what is immediate progress? Or progress for that matter?
Immediate progress is one of the hardest things to see sometimes – especially when working on something for as long of a time span as picking up a new language takes. Immediate progress is the progress you make in a short amount of time. This amount of time is somewhat arbitrary – say a day, or a week. In the span of 2,000 kanji, 25 a day might not seem like much. And by itself, maybe it isn’t. But progress is progress, even if that means you’ve learned two kanji.
Keep in mind that any progress is good progress. This doesn’t mean slack off, though. If you stick with a rate of 2 kanji a day, it’ll take you well over 2 years just to get through them! If you stick to about 25 a day, you could finish in as little as 2-3 months. A faster pace could lead you to be done in around a month.
However – moving so fast that you don’t retain what you learn is pointless. You’re far better off taking on a smaller amount at a time if that’s what you can effectively retain at that time. Otherwise, you’ll forget it in a week. Let’s not forget that you have to constantly review what you do know so you don’t lose it. That would be bad. Very bad.
So if I progress faster than you, don’t worry about it. Just as I wouldn’t beat myself up over someone learning faster than me (let’s face it, I’m sure there’s a lot of you that will, and that’s okay). I’m no smarter than your average person. I’m no smarter than you.
Another point here is that it’s completely pointless to compare your rate of learning with others (Why have I said point twice in the same sentence?). Anyone can cram an hour before an exam, ace it, then forget it completely a week later. I’d say you shouldn’t compare anything at all with anyone else, but if you must, focus on retention, not speed. The real measurement of your progress, however, should be taken against your previous progress. That is, if you knew 400 kanji last week and now you know 600, that’s a pretty good measurement of progress.
To sum it up, don’t rush it. Before you know it, you’ll be there at the finish line and ready t move on to the next task.