When you say 20 per week, what are you learning exactly? Is it just the meanings of the characters or also the readings?
I sustained 50 per week (meanings only) for quite a while, en route to learning all the Joyo kanji, which I finally completed. I did not use RTK, however. I believe it uses mnemonics, which I don't fancy at all, though obviously people differ.
However, the biggest problem is not learning them, but remembering them, if you get what I mean. The more you learn, the more effort it takes just to keep from forgetting what you've learnt. When you get to thousands, it takes forever just to revise all of what you're supposed to know. I have a big tub of cards, with all the Joyo kanji, and when I have a couple of minutes I grab a handful and revise them, then put them in another tub. When I get to the end, I start over again. When I neglect this, it is distressing how much I forget in just a few weeks.