Hello!

I'm on the midst of applying for my visa form. I am a Singaporean wanting to visit my girlfriend who is teaching in China. By default if i were to apply a tourist visa, i'll get 30days. However, my partner has wrote some sort of a letter of her residency during my period of stay. Is the letter going to help me, if I would like to opt for a longer more period of 30days? I would like to apply for 60days on my tourist visa.
Is this reasonably possible to ask for 60days? Or 30days is the only maximum per stay and I shoudn't ask for 60days as my visa will probably be denied anyway? Even with a letter from partner? Is there any viable way of getting more than 30days?
Thanks and appreciate the help :)