Well I normally try to refrain from asking this type question. I just rent the gear I am looking at and get a hands on evaluation but my time is limited and rental companies won't deliver to my location. I was just planning to attend the sporting event since I am really not prepared for it but I got my hands on a 200-400 f4 VRI for a couple of weeks and have a desire to put it though its paces. I had already purchased my ticket for the Bahrain Gran Prix Formula 1 event. I don't know my exact seat location but if I get this chance doubt I will be in my seat (probably pretty far back in the aisle so I am not in the way). I did ask to make sure I could carry it in the event, I was told it wouldn't be an issue. Any one that has been there before feel free to let me know otherwise.
I currently have with me my trusty D700 but not sure if that will be enough so here is where I ask someone who has experience with both cameras to give me some valuable input on my situation:
I would be shooting motorsports at night.
I would assume the track will be lit up pretty good though but its not natural sunlight
I will be roughly 800-1600 ft away from my target(s) according to google earth (where they won't be behind a fence and actually might be eye level at this point)
The targets will be moving roughly 190-230 MPH
The targets are aprox 18 ft in length and 4ft high
I have practiced a bit of hand holding with the lens, during the day I was fine, at night well VR is good but not that good. I have a tripod but doubt I would be able to set that up, figure the lens is bad enough. The areas at night I have to test are not that well lit though so figure I have a better shot at the track Vs a normal street with two lamp post over 100 yards apart.
Where my thoughts are at the moment. I have a lens that gets pretty good "reach" but the DX crop factor would probably help and the ability to crop if need be with the D7100. I think the AF of the D7100 might actually be a bit better than my D700 since it can focus down to F8. I am wondering if the ISO of the D7100 can match the D700 (it might be better but this is the personal experience part I don't have). I did not bring the battery grip with me so I am limited to 5 FPS with the D700 but the D7100 can at least do 6 FPS. The only thing that will drive me nuts is the menu system, I hear its similar to my D7000 but not exactly the same. I worry about the buffer size but a few shots are better than no shots at all. It might be wise just to have a backup camera since my D700 is over 3-4 years old. The only other camera I have with me is a D200 that has been IR converted, that's not going to help me here.
I know it might sound crazy to purchase a camera for one time use mainly but when I return to the US I would sell my D7000 and keep the D7100, the cost of the ticket is more than I would lose on the purchase even if I just sold the D7100 right after. It would cost me more than a D4 to return and try to attempt this again much less the luck of a 200-400 F4.
As I know my seat location and go out to the track before hand and watch some other racing events that are combined I will get some practice. I figure my best bet might be to find a good "spot" to trap focus and have a decent back ground. The other option but much more involved would be panning, which might be my only option if the ISO can't hold up at night but might make better shots anyway.