Am looking to buy a Sigma 150-600 zoom lens for my Nikon’s. There are 2 versions - Contemporary and Sports. I will be shooting motorsports, music festivals etc with this lens. Is there a big enough difference between the 2 lenses to justify buying the sport version which seems to be around £450 more than the contemporary. Both models appear to be FX but seem to have different optics And take a different sized front filter. Can anyone explain all the differences please? TIA.