as you were having issues with lag, id recommend not to use Monster, Now i know allot of the members of the FTB community have become a fan of Reika's mods, However as a server admin dealing with the nightmare that is monster id recommend against it, Reikas mods are laggy, whether it be the WAY Over populated rainbow forest from dye trees mod, or Rotarycraft/ReactorCraft machines that are very tick heavy on the server. Now I do admit there is allot of cool toys procided by these mods, so its up to you to way the pros and the cons. Honestly I hope reika gets around to making his machines more server friendly.
But honestly, If you would like to keep the Community you have, let your community decided, perhaps they will be intrested in some hardcore Blood n Bones, or perhaps they are a direworlf fan and would like to follow him in his single player series. So id suggest pop a pole up on your server forums, give your members a choices of every play possible, let them give imput, as the general Opinion of the members on the FTB forums here may differ from theirs.
If your strongly motivated to do so, you could make your own pack, keep it uptodate, and take your users input on what mods to contain.
All input is appreciated. Thanks guys/girls