AS doesn't really mean anything. 6 AS would be less impressive than the standard 4 AS level candidate not dropping any and achieveing 4 A-levels.
Personally I took 5 AS levels but that's because Further Maths was run outside my Sixth Form by an external party over 2 years rather than as a normal AS on my Sixth Form timetable. I dropped one other AS meaning I had 3 A-levels.
I got 5/5 offers from uni so that was fine. If I wanted to go to Oxbridge or somewhere it would have been obvious by the time I finished my AS and I probably wouldn't have dropped the AS (or in actuality taken up another AS as my 6th form discontinued the subject at the end of the 1st year, was the one I would of dropped anyway) or I would have gotten 3 amazing A*s which would have been easily enough because if I was an Oxbridge candidate I could of.
You're better off focussing your energy on 3 A levels and blitzing them with great grades. A* at GCSE doesn't mean anything btw don't think you're above all this and dive in too deep (don't spread yourself too thin and then mess up with information overload, cos if you do thats the grades the universities you're applying to will be seeing). Take 5 AS if you want and then you can decide which to drop and continue with your favourite 3 as the first year is really just a warmup. If you focus your enegry on Physics and get an A* at A-level with 2 A's in other A-levels, and also have a Further Maths AS under your belt with another AS, combined with a good personal statement you could get into anywhere even with 4 AS's you could easily