Normal Guards get:
1 Firing Positions
2 .88 RA, 1.14 acc, 1.1 pen
3 .75 RA, 1.14 acc, .8 cd, +25% button duration
2560 xp required for vet 3.
Assault Guards:
1 Flares
2 .71 RA, .75 cd
3 40% acc, +25% grenade range
2880 xp required for vet 3.
Assault Guard vet is basically the same as Shock Troop vet, but has higher requirements (2720 for them).
Seems fitting for the unit, and not overpowered. The requirements had been too high, but might be more reasonable now that the squad deals a lot more damage.
Flares are boring for an elite unit and should be replaced with something more fitting, like what was was done for Shocks and Penals.
Assault Guards have worse RA than normal Guards at vet 3 with 0,71 vs 0,66. I'd rather see them give up their slightly better accuracy bonus of 40% vs 30% for more durability.
You're right about the Veterancy requirements. They seem a bit high, but propably don't need a change now that they have three Thompsons.