A 95 average is tough, and depends on a lot of different factors. Lecturers, the amount of scaling (much less scaling in uni than in HS), etc. Given that you're looking at PhB, I'd say you won't have too much trouble hitting 90-100% on all the *assignments* for the first couple of years (assuming a decent amount of work).
Labs tend to be more difficult to get good marks on -- I'm not really an expert, since I skipped first-year physics, which is where you do a fair bit of lab work. I certainly found that it was difficult enough to hit the 8/10s on the second-year labs, and I haven't done any third-year labs yet (being the theoretician I am
).
Exams can be volatile, but in general, doing a reasonable amount of study will get you a decent HD-band mark (decent being 90+). Some lecturers scale the exams, quite a few don't (for example, a lot of the physics lecturers tend to avoid scaling if they can help it).
All that aside, a 95 average is possible, and I encourage you to go for it.
Your aims are something you should set for yourself -- hit the first semester of uni running and then adjust your targets once you get into the swing of things.
In terms of grasping the material, you should find the first-year stuff quite easy to cover, even though you may be learning new material -- the first year is all about bringing everyone to the same standard. Second year is where they really get into teaching you new stuff, and then there's a marked jump from second to third year. (For comparison purposes: first-year classes in maths and physics typically have ~300 students, second-year classes in physics have anywhere from 30 to 60ish, and third-year classes tend to vary quite a bit, but under 30. Some classes have been known to have three students or so.
) Use the spare time to get ahead.
