I would:
Drop the missile teams (shock horror, normally I love missiles) for some points to go elsewhere. In 1200pts there wont be many tanks, and those that are present will be at either end of the spectrum, and while you have 6 mortars, the missiles differing roles are not needed as much.
With the added points boost the 2xHB1x Autocannon to 3x autocannons.
Give strakens CCS a lascannon and make use of the BS 4.
Get grenade launchers everywhere you can, they are good stuffs. This includes swapping out your CCS snipers with grenade launchers. However if you really want them, get a veteran squad with 3x snipers and a missile launcher. More accurate (BS 4) ala more chance of rending, and can hurt anything the missile launcher shoots at bar AV13+. Give them shotguns for a more counter attack role should you wish (2x S3 shots before they charge pretending they are spesh merines)
One commisar would go a long way, it gives you the option of a big stubborn blob.
You can also drop lots of your voxes, if not all. Why? ATM Straken does not have a vox (rofl, typo I bet) so his dudes may have a radio, but he is just screaming across the battlefield. And secondly, you have a regimental banner that allows re-rolls anyway, in a list that will for most part be within 24 iches of each other to benifit from orders and Strakens boosts.
As is, an easy 3/5. I would still 3 it if you took my suggestions on board.
Why? Big blobs, without the stubborn commisar and big chunk o' power weapons make them a LOT weaker then they could be. The most obvious weakness is that they can be swept away should they lose a combat.
It could have more big guns, it is a gunline yet it wont blow away an opponent first turn, on average anyway. It makes for a decent game. Besides your HWT's which can be instant deathed by s6, you have no other way or hurting big things, tanks or MC's
besides spam. Grenade launchers will help somewhat.
YThe 1500pts version I have often played against is a 1-2/5 but this is nice.
