Benchmark: timing 7000 iterations of OP best: get_proparg_new, my best: getpropstr, orig-arg2, yours...
OP best: get_proparg_new:  3 wallclock secs ( 2.39 usr +  0.01 sys =  2.40 CPU) @ 2916.67/s (n=7000)
my best: getpropstr:  4 wallclock secs ( 1.72 usr +  0.01 sys =  1.73 CPU) @ 4046.24/s (n=7000)
 orig-arg2: 12 wallclock secs ( 9.71 usr +  0.04 sys =  9.75 CPU) @ 717.95/s (n=7000)
     yours: 12 wallclock secs ( 9.69 usr +  0.03 sys =  9.72 CPU) @ 720.16/s (n=7000)