Just thought I'd add a little update after spending a bit more time with the Depo and HID setup.
I think my initial disappointment was down to the fact it was more dusk than dark - maybe the colour temperature of the bulbs makes the beam a little less obvious in those conditions.
Since then I've done a fair bit of night driving, and actually, they're pretty damn good. There's still scope for a slightly whiter bulb, but the current ones don't seem too OTT blue. I managed to find a wall in a carpark to test the beam pattern and it seems good. Nice cutoff and height - although I'd like to get that confirmed at my MOT place. I haven't had any oncoming cars flash me or anything, so I'll loosely assume things are as they should be.
Overall, I'm happy with the upgrade.