in 17.5 or even 13.5 you dont really need high downforce. not sure where the amr fits into that scheme but the r8c blackart is considered low downforce which should work better in slower classes.
ive never really had a chance to mess about with pf bodies in 1/12 but never had a complaint about the blackarts. guy in our club sells them and they are very popular.
though i am still looking for a good body for modified. probably stick to the blackart bomber but meh. they just dont last and i cant afford to have $100 in experimental bodies on my bench heh.