I think you really need artillery as a guard player, being able to hit anything on the table is a very useful thing to be able to do..... especially against armies like eldar and marines who like to hide and wait, having the threat of a barrage or two to drop on their heads forces them to move around a bit, I'd drop the unmounted stormtroopers, buy some griffons if you want, but I'd buy a hydra battery to guard your artillery/deathstrikes from planes (almost guaranteed they will be a very early target and you're normally going second as the guard player....)
something along these lines:
REGIMENTAL HQ [600]
Supreme Commander, 12 Infantry, 7 Chimera, Hydra, Griffon Battery (3 Griffons)
INFANTRY COMPANY [300]
Commander, 12 Infantry, Hydra
TANK COMPANY [700]
10 Leman Russ, Hydra
STORM TROOPER PLATOON [350]
8 Storm Troopers, Valkyrie Transport
ARTILLERY BATTERY [250]
3 Basilisks
SENTINEL SQUADRON [100]
4 Sentinels
SUPER-HEAVY TANK PLATOON [200]
Shadowsword
DEATHSTRIKE MISSILE BATTERY [200]
2 Deathstrike Missile Launchers
FLAK BATTERY [150]
3 Hydra
THUNDERBOLT FIGHTERS [150]
2 Thunderbolts
screen the deathstrikes and artillery with sentinels, keep both close to the hydra battery, keep the tanks with open fields of fire and in support range of the two mechanised formations (reg HQ and stormtroopers), it's tempting to keep the stormtroopers mounted to give them a huge engage range, just be wary of any potential threats (aircraft, artillery, sneak attacks) I'd always put the stormtrooper commissar in a valk so when they all die, you'll have a super quick fearless skimmer to zip around, use the shadowsword to take out RA targets when possible, and also to try to threaten war engines, a 1-2 with the tbolts to strip shields followed by a retain and sustain is a great way to hurt/kill warhounds and the like, oh and almost always go all out with the valks rocket pods when you get the chance, 8BP disrupt is a great way to put a dent in almost any formation
the only problem is speed, you're not going to win any sprinting contests, so make sure you try to protect your Reg HQ and stormtroopers as they're your only real hope of nabbing the blitz.... sure you don't want to include some warhounds?
