Ive used pulsin before on some tv remote learning projects, and even at 40Khz, it's fine. I think it's like 600Khz or higher that the chips start having issues at 20Mhz, and 200Khz at 400Khz, so for most things, it should be fine unless you have a lot going on in the loop which eats up alot of cpu cycles. if that's the case, you can have it run on an interrupt and store the pulsin value in a value to read after you get 8 or so bits (the size of the input string).