Ok. So I installed the new antenna today. And the results are [drum roll]..... Well it performs as good if not a bit better than the Radio Shack 800Mhz tuned ducky antenna. So, that is good news.
One odd thing though. The Ebay auction said the antenna model is a "BS800SN-B" 825-866 MHz 4dB. And the sticker on the bag had that model number also. However I cannot find any reference to this model on the Comtelco website or anywhere on the net. They do offer that modem in an -A, -C and -E. The -C says it's for 825-896 Mhz.
http://www.comtelcoantennas.com/bs_800_900_mhz.htm
So I'm bit confused that I cannot find any reference to the model antenna that I have.