Ok, comparison brought forward (the electrician left a fitting and an array of lamps behind & Mrs MV & I just played with them for half an hour)
Conclusions: the CFL is a lot warmer and way dimmer than the existing 50W GU10 halogens. And takes too long to come on; it'll be fine for the rest of the house but not adequate for the kitchen
The 8.5 W LED is a lot brighter; dimmer than the halogens but still way warmer.
The surprise was a 6.5 W "cool white" LED. This was comparable in brightness and hue to the incandescents and to me looks a better bet for the kitchen.