In GURPS Powers it received the Force Extension enhancement.
It also specified that Talent could improve the speed of size change.
In http://forums.sjgames.com/showpost.php?p=563199&postcount=7 Kromm allowed Extra Arm to borrow that.
Technical
GURPS Martial Arts: Technical Grappling 27 re Constriction Attack:
- To effectively wrap around the target’s torso, you must either be of his SM or larger, or have body parts proportional to such a SM due to Stretching, the Long enhancement on limbs, etc. Treat the victim’s limbs or neck as two SM smaller.
Quotes
PK
http://forums.sjgames.com/showpost.php?p=1166684&postcount=2 mentions it takes 3 levels of Reduced Time to change 3 SM instantly.
Unofficial FAQ
http://forums.sjgames.com/showpost.php?p=419825&postcount=5
by vicky_molokh
Limbs with the Long enhancement vs. Stretching: Why are long limbs, at some point, more expensive than Stretching?
What's the point of buying many long limbs instead of a single instance of Stretching and some Swing-only Striking ST? For one, Stretching requires a turn of Ready per SM change per limb to activate. And no, you can't circumvent that by taking Always On: that makes as much sense as Always On Shrinking or Growth.
Second, Stretching doesn't provide one benefit of Long limbs: Long limbs get their HP multiplied by their linear size, as appropriate for their relative SM. E.g. a SM+1 limb gets ×1.5, an SM+2 one gets HP×2, an SM+6 gets ×10. Do not forget that limbs have a ×½ multiplier relative to body HP by default (e.g. 5 HP for a 10-HP character).
Kromm
http://forums.sjgames.com/showpost.php?p=440568&postcount=12
Long limbs, though, come with the implicit promise that they have muscle and substance to match their size. This is why, for instance, long arms get bonus swing damage while stretched ones don't. Ergo, they have solidity that befits their size, and should have HP to match. The rules omit this, but if ever we get a set of rules for dwarfs, giants, and their equipment, then they'll need to cover outsized limbs, too
we're discussing outsized limbs here, not proportional ones. When you buy arms or legs with SM +1 or more, you don't become a SM +1 or larger creature.
You have oversized limbs. So the limbs have HP comparable to those of a larger creature, even though your torso, head, etc., don't.
That's why ×1.5, ×2, ×3, etc., to the crippling threshold makes sense for limbs that have SM +1, +2, +3, etc. An SM +1 creature would have 15 HP, if built like a human, and require 8 HP to suffer a crippled arm.
If you stick his arms on a SM 0 man with 10 HP, then they should still require roughly 8 HP to cripple.