2X-TC and The Sigmonster?

I was just thinking about using a 2X on my 8oo MM Sigma and was wondering if any one else was this crazy. I have used the 1.4-TC with very good results. Ever stack the two? You see there is this tiny bird way up in this big tree.........

There is a fellow at the Gilbert Water Ranch, where I do a lot of avian photography, who has a Sigmonster. I can't remember his name offhand but he and I discussed the Sigmonster when I first decided to get into avian photography. He stated that the Sigmonster yielded "OK" results with the 1.4x tc but the 2x tc yielded totally unacceptable results. This is pretty much in line with the use of 2x tc's on zoom lenses. I can't even begin to imagine what stacking 2 tc's on the Sigmonster would yield as far as IQ goes.

Thanks Tom, I wish I had a bit of your clear ,dry air to shoot in sometimes.

You are more than welcome to come out and sample our dry air, Robert. August would be a great month.

My farm is running wide open this time of year. Last year from the first of March till the end of October I had one day off. I turned 55 last week and worked 18 hours on my birthday. Thanks for the invite and if you are ever over this way in the Winter time holler and I`ll find you something cool to shoot. Some day when I sell this place I want to come see your cacti. I had over 200 species in my greenhouse and lost them in the freeze of 85. My sister has a yard full of cacti now that are Winter hardy. You can see my farm at www.rainbowranchtrout.com And we open in a bit so off I go.