I've already written this message but seems there are some problems with the host so maybe it didn't arrived well on the website...it will be a pleasure for me to repeat it
I disagree withthe common strategy.
I would consider :
1-15 : slow
15-27 : fast
27-end : normal
Why ? Because you have to remember that there will be around 9 experimental questions in the quant section. Those experimental are there to be tested, after that ETS can check their level of difficulty, see if the formulation was good, see how many people answered well, etc... For all those statistics, they need a maximum of people to answer it in normal conditions.
It's quite sure it won't be in the first 5-10 questions which are very important to determine your gross level....in the other hand, it is also sure that those questions won't appear at the end of the test because a lot of people won't finish on time or will rush by guessing at the end of the section and ETS is not interested in this way of answering. If they want to judge correctly the difficulty of the question, they need people to take normal time to answer, not to guess.
That's why I think that the last 10 questions will definitely be important too. I am quite interested by the GMAT Club members opinion on this subject because I may be wrong with this strategy, I am just curious about what you guys think about this...