Hello All,
Thanks all for the valuable suggestion. Yes..the Sigma lens is not that great ..as were with some folks at the Airshow 🙂
I had been on Saturday and Sunday, so I’ll shoot on Saturday, learn from the mistakes and correct on Sunday.

On Saturday it was fully clouded and on Sunday it was partially clouded, and in my excitement I did lots of mistake in metering (Centre weighted, Manual, ISO 400 (mostly) ) .. after every series of photos I would examine the histogram and the subject to see if I did any mistake, and try to compensate in the next shot.
White balancing was mostly in setting for Clouded, except on Sunday where some times I changed to sunlight.

Also as the direction (I was pointing to) changed so did the light intensity on the subject there.. well I don’t know how to adapt to that.

About the metering, I would look at some grey cloud (that I would guess to be at 18% grey) and get the metering, shoot some shots, quickly check the histogram and see if some details was available of the subject, Well the LCD display on 400D is not that great, but Okay for an amateur like me.

It was a Great experience, here are some of the photos I uploaded. Did some resizing due to size limits using MS Paint.
http://www.flickr.com/photos/14497022@N04/

Thanks
Vignesh