How tall to grow my tomato plants?

My tomatoe plants are currently 6-7' tall and they do have tomatoes ( all be it not yet red). I was wondering if I should cut the top of them off? My thinking is that, the plant would divert its energy to the tomatoes? Is this correct or should I just leave them or do something else?
Thanks

 

There is still plenty of time for tomatoes to form and ripen. I would let them grow until at least the end of August, unless they get too tall to maintain. You could also top them now and let a side shoot or two develop for more production.

 

Envisage the latest date you are likely to harvest tomatoes (usually first frost) and top the plants six weeks before this time (make that eight weeks for particularly large fruited varieties).

 

I have topped mine. The consensus among my gardening friends here in Vancouver is that any flower that forms from now on is extremely unlikely to produce an edible tomato before the autumn rains start and the inevitable blight hits your plants. I grow mine under cover which largely prevents the blight so I can extend my picking season into October but the harvest that month is extremely modest.