That looks very iffy to me, what's the old saying?
If it looks too good to be true then it probably is.
It'll be great if it's genuine though.

From my limited use of the 150-500 I'd say the lens OS works better the the SR on the longer focal lengths would you agree Mike?

What lens are you currently using?

You won't regret getting the 70-200 it's awesome, especially its AF speed, as you know the K-7 is not exactly lightening on the AF front but with the HSM it's great. I do shoot on continuous focus and hi speed and tend to take a burst of shots as the karts or cars head towards me and tend to get some in focus and some not but the HSM does a sterling job. I do believe that the additional OS will make a huge difference.
As for shooting wide open, it's not worth it as you are going to struggle to get enough of the vehicle in focus, and by stopping down you get a slightly bigger DOF to get the point of focus right. I tend to use f3.5 up to f5.6 to help keep the shutter speed up and I soot in TAV and fix the graining later. Better to have a grainy sharp shot than a blurred smooth shot, I notice you have a 20d so the same sensor as me and hence the same noise levels.
Once I used the 70-200 it made a huge difference to the IQ of the shots I was getting to keep from the karting and with OS this will be better again.
In short it is a great lens and I would recommend it all day long.

These were taken with OS (on a 150-500 though)
link

Number 1 is one of the best shots I have ever seen of the NL

Hi Mannesty,
I Have the non OS version with HSM and it is a cracker.
I too shoot a lot of motor sport, albeit at the smaller end, and its AF is very good IQ is excellent, I have just got my hands on an OS version of the 150-500 and am now looking longingly at the OS version of the 70-200 as it makes a big difference to the number of "keepers" Examples
Buy it now, before you change your mind, you won't regret it.

4 is a stunner Mike, great movement in the legs and tack sharp where it needs to be.

Lens received Friday wonderfully wrapped and promptly delivered and in great nick, a great transaction...
Cheers Lloyd

I have one of these, be careful! it is so sharp you'll cut yourself if you are not careful

Lovely vibrant shots