I let mine almost reach the glass and then remove the tops I suppose the amount of trusses depends on the distance between them.
Out side I stop a lot sooner as I normally end up having to pick them green and letting them ripen off the plants and towards the end of the season I find the don't ripen so well.

I stop mine at 4 - find you get better fruit

I'm currently growing GD myself outdoors. 2 trusses are setting with 4th truss visible.

The main factors are as ever temperature and light conditions. With a decent summer grown in direct sunlight for at least half a day, I'd grow to 5 trusses indoors and 4 outdoors. If you intend to harvest until October perhaps add one more truss to develop, particularly if we get an Indian summer.

I leave mine until they run out of growing space as well, I think its a case of personal choice, I guess its different if one wants the perfect size, shape and taste to enter into a show....

Thanks for your replies, I can see stopping them sooner outside, depending on the weather.