I strongly suggest your guild to try 16 man if you are in love with true challenge.
We'd love to, Dalborra is a quaint little server, on the opposite side of the world. Our Wookies hang upside down in their trees and numbers are not looking so rosy lately. We've scheduled 16m raids but getting the numbers requires us fielding casuals and PvPers complete with their uber BM gears. Many of them quite inexperienced in all things PVE too. To top it all off, 2 of our core members have been having grave internet issues lately and further making matters trickier when it comes to putting together a competent 16 man group.
What would be ideal would be for Bioware to TEST their operations, balance properly and then put it live. Blizzard released a lot of ill-tuned encounters too, but they got it right most of the time, Bioware hasn't. Especially true when you compare how they've tuned 16m v 8m in the last 2 operations they've released. 16m TFB was vastly easier than 8m for the first 3 bosses, now the shoe is on the other foot for EC NiM, where 8m was a cake walk.
I accept they're not going to nail it exactly with the balance thing between 8m/16m and tuning overall, but surely they can do a better job of it than they have to date.