Looking at it, I have about 10k files and it is only using about 12% memory, perhaps not as bad as I thought. 50k should be absolutely fine I would think. Here is the output of top showing btsync at idle:

    PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND
    2993 btsync    19  -1  122m  60m 2988 S  11.9 12.4 610:05.84 btsync

I have noticed that the CPU takes a beating during any sync operations, tends to grab 100%. I limit the CPU for the btsync process to 60% max and also overclocked the Pi up one level (after installing a heatsink kit). Here it is during typical filesync operations:

    PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND
    2993 btsync    19  -1  122m  60m 2988 S  63.8 12.4 612:51.33 btsync

To limit the cpu I use cpulimit and put this in my /etc/rc.local

    /usr/bin/cpulimit -e btsync -l 60 -b >> /dev/null