Megaman 14W GU10 replacement?

Not possible with CFL. You would need to look for a metal halide discharge lamp around 35W, but I don't think you'll find one of that power which is as small as a GU10 mounting hole. There are some lower powered metal halide lamps available too, but I can't recall what the lower power ratings are. They are roughly 3 times more efficient than a filament lamp (probably better than this at these lower power ratings where filament lamps are particularly inefficient) and available in a variety of colour temperatures. They need control gear and a different fitting, so it's not a direct swap.

For CFL replacing a GLS filament lamp, it's about a 1:4 ratio. CFL's make poor refector lamps, particularly in a form where the tube is physically a significant size compared with the reflector as in any small reflector lamps. In this case, the ratio is going to drop very significantly, probably to around

1:2. So I would expect a 14W GU10 CFL retrofit to be roughly equivalent to a 28W filament lamp. However, they can often appear better than this because that are flood lamps (rather than spot lamps), and the wider coverage can mean better lit walls and indirect lighting as a result.

I fitted 5 of the Megaman 7W GU10 CFL retrofits a year ago in a friend's house. They get a lot of use (in the main thoroughfare of the house which has no natural light) and none have failed in that time. I can't tell if they've dimmed as I don't have a new one to compare with, but they don't seem dim, so I suspect they haven't significantly. These were the lowest power rating ones I could get at the time, as whoever originally installed the GU10 downlighters had installed more than were really necessary.