Well, yes, every piece of it effects how well the dog turns and moves. But remember there is more to it than just rear angulation. A lot of the WGSL dogs *don't* have the extreme rears of the American show lines but they have extremely steep croups which gives them the "banana back" look (curved back that just sort of drops off).
In general, the rear angulation needs to match the front for the dog to move well. How much angulation there should be depends on preference, but if it doesn't match it doesn't matter how much or how little you prefer the dog will not move with balance.
Liesje & the K9s
Nikon (GSD) U-CH SG Alta-Tollhaus Bono SchH1 KKL T1 FO PA TF-III FDCh-S CL1-R UJJ U-CA HIT TT CGC
Coke (All-American) VPC's Coca-Cola CGC, couch warmer extraordinaire
Indy (All-American) Blue Horizon's Indigo Girl, flyball star in training
Rainbow Bridge Kenya (GSD) U-CH Alta-Tollhaus-Krieger Lamb Chop CL1-R CL1-F RA HIT TDI TT CGC
vom Blauen Horizont / Blue Horizon GSDs