So I wanted to play some assassin chick when I picked up this game. But checking the internet I saw many people say Khajiit or dunmer are better for stealthy classes. What do you guys think? Would playing as another race then the one with the best bonuses for the specific class I want to play make the game too hard for me? This is especially important as I want to play on master difficulty.
Regards.

the race choice doesnt really matter in this part of the Series, you can pick whatever race you like, unlike say, Oblivion or MW

Well I went with breton for the magic resist for my assassin. But I think the best would be dunmer for the fire resistance, then you can become a vampire early on and the fire weakness won't matter. Vampires get a bonus to sneak and illusion, amongst other benefits/drawbacks.

really? no. or at least, only just a tad.

Please, for the love of god, play whatever race you want and disregard bonuses completely.

Not if your not an Altmer

Some races start out at higher skill levels in certain areas then other races, and all races have a specialty, aka. woodelf and archery, however nothing restricts you from doing otherwise =)

Playing a race with attributes you want can certainly enhance your experience, but as Sentenza said, it is not really a requirement. Any character of any race can become a master of almost everything in Skyrim.

After 1.2 it doesn't really matter anymore anyways.

Minor bonuses can be had by selecting the 'right' race for a specific class. By 'right' I just mean the ones whose racial abilities mesh well with the playstyle of the preferred 'class'. But it makes very little difference in the medium-long run. Your massive, 7-foot, heavily muscled, metal-beard wearing orc can still be as stealthy as the sneakiest dark elf with practice and training.

Khajit, Breton and Orc are the only ones with worthwhile racials. Breton and Orc ones make a HUGE difference. Khajit is nice... I haven't found any sort of night eye spell/potion so they are the only ones with it that I've seen but it's mostly convenience.

Thanks a lot for the responses guys. Wanted to ask one more thing;
Which racial will help me most as an assassin?

don't look at the skill bonus. But if you want to differ them, look at the special abilities.

Orc, double damage racial with sneak attacks is great

I agree 100% the racial skill bonuses dont matter at all half an hour into the game but the racial special abilities do matter . The orc racial ability is very powerful and magic resistance is pretty sweet as well or +50 magicka is not too shabby either if you ask me. The fire resistance for dunmers is usefull if you want to play as vampire. Kahjiit have the most useless ability imo since the game is already rather bright so no night vision is needed... So go with whatever race you like the most but take a good look at their racial abilities before deciding.