a) Give me 5 minutes so I can show you what I've been developing so far.
b) Give me 5 minutes so I can show you what I've developed so far.
I am bit confused which one should i use present perfect or perfect continues?
I see this differently from Teacher KSHuang's answer.
"So far" means up to this point, which implies that something is not yet complete.
"Developed", past tense, implies completion, so "what I have developed" is different from "so far". "What I have developed so far" refers to the completed portion of an unfinished job.
"What I have been developing" is more ambiguous. It refers to something ongoing, but it could now be at any stage, from just getting organized and started (conceptualizing), to just finishing. So "what I've been developing so far" refers to unfinished work of ambiguous status, potentially including not actually having any portion completed.
Short Answer: I agree with the commentators that they are the same and that I would remove "so far" for the first sentence because it's already implied by the word "developed."
Long Answer: If you're looking for something more colloquial, I would have said, "Let me show you what I've been working on."
Or if you really wanted to use the "give me five minutes" line, I would have said, "Give me five minutes and I'll knock your socks off," because if someone said to me to give them only five minutes, I would expect to be impressed, but maybe I've been watching too many infomercials.
Otherwise, your phrasing was fine.
a
.