I've had all the above antennas mentioned....forget them all and go for a Sirio Gain Master..beats the lot of them...Friend of mine has a Sigma IV on test against a SGM at the moment along with his 3 ele beam, and one vertical has to come down, and its not the Sirio

My own 827 was taken down in favour of the SGM and WOW the difference is clear ...the SGM has out performed any other vertical on local and DX work.....plus a flat VSWR from 25.500 to 29.800.... read about it here
http://www.gain-master.it/