Grade 6 is quite different to grade 5 because, like everyone has said, you can't just play the notes in tune and at the right time. They have to actually start meaning something, and it all needs to sound more like a performance. On violin in particular, to make your playing sound really good and expressive, you need a good solid technique first, so I think that should be the first thing to go for. Vibrato is a must! Not necessarily on every single note, but when you're playing a slow piece, or holding a note, they will expect it. Double stops start coming into play at grade 6 too, which will test anyone's intonation.
I'm afraid I never actually did grade 6 (or 7) so I don't know the scales, but I imagine you should be playing a few 3 octaves scales in major and minor (harmonic and melodic), starting dominant and maybe diminished 7ths (possibly just 1 octave though), and no doubt some octaves sclaes, but not just straight octaves, probably playing the bottom note, followed by the top note in a slur, and then with a new bow, both notes together. I'm sure the syllabus is online somewhere. I do recall that part of the Dvorak Sonatine is on the list, that's a great one to learn

I've probably already mentioned it, but it really is great fun!
Go for it VN - at your rate you'll be doing the Bach soon enough, and it will be worth it. I'm re-learning it (yay!!) to play at a concert right now, it is a lovely piece

Maybe you could set yourself little targets each week, like 2/3 scales a week, and decide when you want to finish your current pieces by, then you will be able to see when you could start the Bach, which would probably get you to your target more quickly, and might make it come quicker, as the end will be in sight.