Even 65536 is likely too high.
quoting: http://www.freebsd.org/doc/handbook/configtuning-kernel-limits.html
The NMBCLUSTERS kernel configuration option dictates the amount of network Mbufs available to the system. A heavily-trafficked server with a low number of Mbufs will hinder performance. Each cluster represents approximately 2 K of memory, so a value of 1024 represents 2 megabytes of kernel memory reserved for network buffers. A simple calculation can be done to figure out how many are needed. A web server which maxes out at 1000 simultaneous connections where each connection uses a 6 K receive and 16 K send buffer, requires approximately 32 MB worth of network buffers to cover the web server. A good rule of thumb is to multiply by 2, so 2x32 MB / 2 KB = 64 MB / 2 kB = 32768. Values between 4096 and 32768 are recommended for machines with greater amounts of memory. Never specify an arbitrarily high value for this parameter as it could lead to a boot time crash. To observe network cluster usage, use -m with netstat(1).
If each cluster represents approximately 2K of memory, 65536 = 134,217,728 bytes or 128MB or ram, just for mbufs. In reality, a bit more than this (65536 * (2048 + 256), so around 144MB) is used.