Don't waste your time and money buying a masonry drill bit. The clue is in the name 'Masonry' that is exactly what it is meant for. They are not made to drill into reinforced concrete (that's what lintels are made of).. also it doesn't matter how far you move along above the window, the lintel will still be there.
When using the hammer action on drill with a masonry drill bit you will find it will bounce around on the lintel as it cant penetrate it and you will end up making a mess.
I fit a lot of curtain tracks and poles and you will find you are not alone with this problem .. the trouble is I usually find the mess after someone else
has had a go (normally hubby).
What is needed is an SDS drill and a 6mm sds bit. This combination will fly through concrete. Mine gets used many times a week and the £400 outlay is acceptable in a commercial environment.
They can be picked up for a lot less ..
http://tinyurl.com/qjsl28m .. but is it worth it ?
The other alternative if you are fitting tracks is to fit a batten fitted into the plaster with short screws and plugs.. then remove it to apply a couple of beads of Gripfil to the batten. When re-applied and dried .. you can tie your horse to it !
If this sounds daunting ... As mastercraft say's .. "Perhaps consider getting someone in".