Yeah I suppose the higher the gsm the better aswell and 300gsm seems pretty good. I guess the best thing to do is experiment with the types of watercolours. I think that's more important if your paper is already thick enough. I find watercolour tubes to have better colours & darker colours compared to the ones you get in pans. Also, unless your going for an oil painting style you don't need much paint for a cool effect with watercolours. Often using the white of the paper looks great with watercolors. :)