I don't typically blow an entire wad in a single round. I like to save Low Slash for when I miss with my standard action, so I can still get my sneak attack damage in for the round.
At 7th level, I was usually doing 1d4+5+2d8+3, for about 20 points of damage in a typical round. Occasional crappy dice notwithstanding, I was at +16 to hit with CA (which I almost always had), so i was hitting most of the time. Still, 20 damage per round doesn't seem particularly high to me for a 7th level striker.
At 8th level I'll be doing 1d4+7+2d8+5, for typical damage of 24. So, in your scenario, if I blow Low Slash and an Action Point in the same round and I have CA on the enemy, and I hit with all three attacks, I rate to do (1d4+7+2d8+5) x2, plus another 1d4+7+5 for low slash, which is an average of 62 points.
If one of the other attacks is Bloodbath, I would do an additional 1d4+7, and then ongoing 2d8+5. That would be an expected 71 points + an additional 14 at the start of the enemy's next turn. Neat!
Also, regarding Slaying Action, we usually have non-combat encounters between combats, so with most combats we earn a Milestone and an additional Action Point.