I have two family members and a friend that all bought the gold package that comes with that coil. I'm using the 10.5" HF DD most of the time. The 5x10 has proven itself to hang in there with the 10.5" DD and one occasion that comes to mind, they actually found some very old coins in an area that I'm positive I went over with my 10.5" coil first. We were detecting in some soil that was pretty noisy and I'm not sure if my larger coil was picking up and rejecting more of the noise or if perhaps they had a little better ground balance than what I did. this was one of the worst detecting spots as far as nasty ground that I think we have ever detected in. We were all hunting in the same pattern mode.
Here is a post that my brother, hotrod53 made the day after he ran circles around me with that coil. Don't get me wrong, I was happy for him to find these coins but I was kind of scratching my head being that I had a year jump start on him using the 705. I think detecting is sometimes like fishing, two guys in the same boat can have completely different levels of success at the same time in the same water. One day you'll do good, the next day the other guy will do good.
http://www.findmall.com/read.php?55,1493694
Don't sweat it, I think you will be happy with it.