Sure, you only have to set it once, but it does not hurt to set it at each launch. keeps the script simple

Doing +x every time keeps the script simple?

Doing +x ea. time:
---------------------

#! /usr/bin/env python3.1
from os import chdir, system
chdir("/home/usrname/Desktop/powder_39.0-dir")
system("chmod +x powder-sse")
system("./powder-sse")
exit()

Only doing +x once in terminal:
----------------------------------

once in terminal:
cd /home/usrname/Desktop/powder_39.0-dir
chmod +x powder-sse

every other time:
#! /usr/bin/env python3.1
from os include chdir, system
chdir("/home/usrname/Desktop/powder_39.0-dir")
system("./powder-sse")

Already packaged with +x:
-----------------------------

#! /usr/bin/env python3.1
from os include chdir, system
chdir(powder_39.0-dir)
system("./powder-sse")
--------------------------------

Is it just me, or does the script look shorter and simpler without applying the +x flag every time before startup?

Other than the use of a couple of doubles there really isn't much that would benefit from a 64 bit build (it's mostly floats and ints) so that's why you arn't getting a performance increase.