Lens Rental Advised?

I have been 100% happy and satisfied with the results of my 70-200 at the track. When extra reach is needed the 2x TC with the lens has worked out great. I know I am sacrificing some sharpness there but as said I am satisfied.

My current work as gotten me to the point that I am shooting Petit for a client. Since this will be my first track work going into print I was thinking about renting a Super Telephoto to get a little different view than I normally have.

What would be your recommendation? Go with what I know and are happy with? 300mm rental? 400mm rental?

Thanks guys!

Don't know if this helps but I was looking to rent a lens for some motorsports photography. I knew that 300 mm would be OK at this track (Goodwood) having used a 300mm there 5 years ago. I went for the 300 F2.8 IS, as I understand that this is the 'standard' pro-motorports lens, but the company rang me to say it wasn't in stock and offered me a 400 F.28 IS for the same price. Initially I said yes but then cancelled, after doing some homework and finding out that the lens weighed 5.5 KG!

Eventually I bought a Sigma 120-300 F2.8 which I'm now going to sell, hoping that this works out cheaper than renting one (I could've rented one for £95).

How about the 300 2.8 with your 2x TC in reserve? Personally, I'm glad I had the flexibility of the 120-300 as in some places, 300 was too long.

Steve