I think the scout tank size is GROSSLY disproportional : at least checking numbers from FMP the scout tank is identical in storage space to a full sized tank. I'd suggest making it 1.5 units, rather than 7, considering its significantly smaller in all demensions. Besides, being able to stock some for base defense would be nifty.
On the topic, isn't 15 hp and 6 rounds a little light? The rounds hit hard, but it seems like a single pistol round can put it out of commission on high damage rolls, while anything else almost promises a death. Id figure a jump to 40 hp would be reasonable, after all, its supposed to be LIGHTLY armored, but besides being able to resist ultra light rounds SOME of the time, it seems incredibly fragile at all other times. At least 40 would give it a decent chance to resist a rifle round once without falling apart. on anything but a lowball.
The 6 round magazine also seems a little light. I mean, it can't exactly reload mid mission. What about 8 or even 10 shots?
I also want to say, the sectoid power shields are horribly over powered. It seems they fully restore after a single turn, which means unless you train lots of fire at them on 1 turn, they wont even be hurt. It wouldn't be so bad if the shields took longer (4 turns maybe?) to fully restore, but it seems like it takes several m60 rounds just to break the shield, much less DAMAGE the target.
Generally, I've found the sectoid ships to be ridiculously dangerous, between the shields and psionic attacks. It takes continued grenade launcher attacks, m60 fire, grenades, just to drop a single soldier. I understand soldiers should be a little hardy, but the sectoids are easily several fold more difficult to kill than gazers in FMP. I think either the total shield HP should be lowered, regeneration made slower than instant, or both. Another idea is to make the shield HP take from unit energy, or possibly even deal significant stun damage when it bursts, so at least bursting the shield multiple times will knock out the user, so its not so cheap.
p90 should have its auto fire mode raised to a larger burst size : p90 is known for its fast automatic fire isn't it?