samoth
In your example, both round inflict stun damage and will not change their DV to physical (even if they exceed AV); check page 168:
"If the modified Damage Value (DV) of an attack causing Physical damage is less than the AP modified armor rating, then the attack causes Stun damage instead of Physical damage."
As you can tell, the reverse is not true. So, you're not going to kill the goon if you use gel and SnS rounds, merely incapacitate him.
Furthermore, the 13S and 11S(e) DV values are resisted with Body 3 + AV 12 / 7 respectively, and the mook has 8+(3/2,roundup)=11 condition monitor boxes; in both cases, your assumptions are a little flawed, statistically. Allow me to elaborate.
First off, hit probability for Gel rounds. Using Insaniac99s hit probability generator, and assuming the mook has all attributes at 3, we see the following:
http://anydice.com/program/3395Probability of attacker scoring the maximum 6 hits: 58.78%
Probability of defender scoring 0 hits: 8.78%
Attackers hits on average: 5.21
Defenders hits on average: 1.98
Attacker's net hits on average: 4.02
Average DV before soak 10.64
Average DV after soak: 5.93
As you can tell, your chances of disabling the mook is statistically not that high with a 7P weapon, as the target gets to dodge and soak. He'd still be knocked over, though, as the physical limit of the mook in this question is 4, and gel rounds reduce this to 2.
Now, let's take a look at SnS rounds,
http://anydice.com/program/3396:
Probability of attacker scoring the maximum 6 hits: 58.78% (unchanged)
Probability of defender scoring 0 hits: 8.78% (unchanged)
Attackers hits on average: 5.21 (unchanged)
Defenders hits on average: 1.98 (unchanged)
Attacker's net hits on average: 4.02 (unchanged)
Average DV before soak 8.75
Average DV after soak: 5.62
The Electricity damage is a little lower on average, but you can also count on it's secondary effects of slowing the target down and making the target worse at doing everything for a little while.