Fast vs Quick

Neither. It's "I was surprised to have recieved your reply so quickly".
(or "so soon").

"Fast" and "quick" are adjectives. You need an adverb there.
Rommie

Fast is an adverb as well as an adjective, isn't it?

He runs fast or does he run quick?

He runs fast.
He runs quickly. Does he run quickly?

Quick is a measure of time; fast is a measure of speed. For example: "My car did great at the drag races today. My quarter mile elapse time was a quick 13.99 seconds, and my speed was a fast 102 mph.

So would you say..."the egg was rolling fast on the table" or "the egg was rolling quickly" in sentence "The boy run up to the opposite corner but the egg was rolling too quick/fast"? Or does it depend on what I want to emphasize..the time or speed?

I've just come onto this thread, so have not read any of the previous posts, but I see no time/speed relationship between quick and fast. Your sentences are synonymous. Since a few people think that 'fast' is casual as an adverb, 'quickly' is slightly more formal. From Macmillan:

Fast: over a short period of time The business has grown very fast.
Quick: do

I think Anonymous is right. In your example, 'The business has grown very fast', the emphasis is primarily placed on the rate of growth (i.e. speed), rather than the length of the period.

I think quick is time of reaction> Taking off on a 100 mts race for example
Fast: Time getting from one point to the other.

Usain Bolt is the fastest, but not necessarily the quickest. There were other competitors maybe quicker in taking off, but he caught up by being faster along the 100 mts.

Hope this make sense.

But seriously folks; I was taught that fast contained a component of distance, whereas quick was simply a measurement of time.