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Just placed the order for my Sigma EX 70-200 F2.8 HSM lens for my D70.
Yeah yeah yeah, its not a Nikkor, but I've yet to read any bad reviews and a LOT of people are saying it's tack sharp, on par with the Nikkor or L series equivalent. Should be here on Saturday so I'll have a chance to give it a go at the BMWCCA autocross this weekend.
I'm going to be getting a TC in the near future but I'm having trouble deciding between the 1.4 and the 2.0 (the Nikkor 1.7 would be a pretty nice alternative... ). Am I right in thinking that the 1.4 would have a maximum aperture of 3.5 and the 2.0 would be 5.6? Any input on the decision? I'm planning on using it for sports like soccer, ultimate frisbee, autocrossing and some track events. The 400mm reach would be excellent but I'm concerned that AF may suffer and that f5.6 may not be enough to adequately blur the background for isolating the subject.
I'm using the TC-17 with my 70-200 VR and they are nicely matched. The TC-17 is actually pretty sharp even at full resolution.
BTW you're maximum aperture is off.
1.4x with an F/2.8 lens is F/4
1.7x with an F/2.8 lens is F/4.8
2.0x with an F/2.8 lens is F/5.6
From what I've heard, the 2.0 imacts the autofocus speed noticably. I haven't had much issue with the 1.7x.
The 1.7x would be a pretty good compromise. You get the extra range of the 1.7x (340mm vs 280 for the 1.4x) and you also get a sharper converter than the 2.0.
When I have been shooting with the 1.7x I very occasionally wish I also had a 2.0 for that little bit of extra reach, but thus far I haven't found myself wanting for a 1.4x in addition to the 1.7x.
Hope that helps a little with your decision making process.
I'm looking forward to some photos from you soon from the new lens.
Should be here on Saturday so I'll have a chance to give it a go at the BMWCCA autocross this weekend. 
). Am I right in thinking that the 1.4 would have a maximum aperture of 3.5 and the 2.0 would be 5.6? Any input on the decision? I'm planning on using it for sports like soccer, ultimate frisbee, autocrossing and some track events. The 400mm reach would be excellent but I'm concerned that AF may suffer and that f5.6 may not be enough to adequately blur the background for isolating the subject. 
