There's something else wrong then, but take out the poppet shelf for a while, see what happens, Like I said, we have three running a bunch of stuff active in those chunks on much less memory with no issues.
Try the poppet shelf in a different chunk maybe?
That's what MC Pro recommends for a FTB server, so we figured it would be good enough for AOTBT, with 33 players slots, and it's run nicely so far. A server doesn't need as much RAM as the client does, I guess.