We are using 1.7.10 and sadly can't use fastcraft due to some nasty bloated stuff were using haha.
But I noticed fastcraft can really speed up the gzip compression of the level.dat or at least prevent stalling while it's compressing it.
By any chance would you be willing to explain what is going on and what change you made? I know it's closed source not asking for the source just so we can look into it and maybe improve our own server.