experience with Metal Halide?

[mexorchid]

I'm missing some proper light for my cattleyas. Reading a lot on the topic, Metal Halide seem to be the best option for me but it's hard to figure out which strength to get.
I want to light an area about 125cm x 55cm next to a north facing window that now in autumn is not getting much sun (days are getting really short in Canada anyway).
How many Watt would you recommend?
And how far over the plants do I have to place the light with your recommended Watt? I also have some plants hanging on mounts over the table. I'm not quite sure what's the minimum distance from the MH light to not burn them.
Heat won't be a problem, I feel always cold myself.
Please share your experience and wisdom with me! Thanks