I do Engineering, and keep in mind this question is subjective - my take. Relative to your HSC, you'll find that a 6.5+ GPA is easier. This is not to say it's easy. The amount of content you'll look at in a term is arguably lower than the HSC. Where you won't find it easy is the time sacrifice you have to make, whether that's in terms of social life, personal time, extracurricular commitments, work or other things. Some people can juggle everything but you're most likely not the exception, and you'll find that your mental wellbeing may suffer for it.