multi hash
is it possible to add few handshakes hash to 1 hash and to run only 1 hashcat instead of 4-5
for windows:
copy /b single_hccapxs\*.hccapx all_in_one\multi.hccapx

for linux:
cat single_hccapxs/*.hccapx > all_in_one/multi.hccapx

If you use cap2hccapx it will automatically generate a .hccapx file that contains all the single hccapx struct in it (i.e. it will automatically generate a multi network/handshake .hccapx file)
bash: all_in_one/multi.hccapx: No such file or directory
You have to mkdir all_in_one of course
I have copied 4 .hccapx files together in hopes of saving time / getting better performance vs running the captures one at a time. However, it seems that its just multiplied the Time.Estimated figure. In fact, its gone from ~2 days to ~8 days.  

Hashes: 18 digests; 10 unique digests, 4 unique salts
Bitmaps: 16 bits, 65536 entries, 0x0000ffff mask, 262144 bytes, 5/13 rotates

Was I wrong in thinking I would somehow save time using this approach of copying the .hccapx files together? Is there anything that can be done to optimize the .hccapx file or the attack parameters when using this approach?  

I must be missing something because it seems like comparing the hashes should be a relatively inexpensive operation compared to calculating the hashes.
If you are cracking different networks at a time there cannot be any speed improvement. The handshake is salted with the SSID.
Ok that makes sense.  I remember now reading that the SSID is used as salt in WPA hashes.  So still have to compute a hash for each network.  Well at least this makes it easy to combine the jobs and then launch it and leave it.  So maybe it saves me a little time.