As a predominantly heavy-class regiment, any 1st Guards formation is going to average out to heavy-weight. Since you've already got one assault-weight lance, and want to include a medium lance in the form of those Wolverines, your third lance should be solidly heavy.
I'd recommend a set up like this:
Assault-weight Fire Lance:
- 2x Stalkers, 2x Awesomes
Heavy-weight Battle Lance:
- Orion, Warhammer, Thunderbolt, Marauder-3M
Medium-weight Striker Lance:
- 2x Wolverine-6Ms, Trebuchet, Hermes II
Or something in that vein, at least. Gives you a good balance of speed, with plenty of both long-range and short-range firepower in each individual lance. Generally, I'm not a fan of mixing speed brackets within a lance, but I stuck the Hermes II in there to prevent that medium lance from becoming too top-heavy (my first idea had been a Griffin). Plus, it never hurts to have a little extra speed every now and then.