I'm in the market for a good quality zoom lens for motorsports, potentially two lenses actually as the tracks I attend differ immensely in focal needs. The current lenses I have been looking at are:
Canon 70-200 f4 (IS or non-IS, still on the fence if IS is worth it)
Canon 100-400 IS
Sigma 100-300 f4
Sigma 50-500 "bigma" (definitely not the fastest but plenty of reach. Unsure about the quality for motorsports applications)
I shot the ALMS @ Mosport with an EF 75-300 USM lens and while I got some good shots, it just felt very soft to me and didn't have the IQ I was looking for (I didn't expect it to churn out top notch shots for a $299 lens).
Any help would be greatly appreciated as I've scoured the forums here and photozone reviews to get a feel of optical quality but am looking for more field experience recommendations.