Seems that either way you do it you'll end up losing out. If mine get too high, i bend the stem at the chosen point till it breaks, that is to say falls over limp, not breaks. It then heals itself but the bent section will grow sideways. Basically a stressful form of LST.
You state that if you LST your plant then you will have to lose a some of the other plants due to the size of your grow room. If this is the case then i would personally either LST them and get rid of the others, or just let them go while accepting that their yields will be hit, or just chop the top off the plant that is too tall. Sure you'll hamper it's yield, but you can then save the other plants you'd have had to remove. It's all a learning process, you win some, you lose some. One of the key things with growing is that until you know exactly how your plants will behave, never overcrowd your grow room.
For your information though, even with auto's, if it states it will grow to a maximum of 1m tall, ignore this, it is bollocks. (unless by 1m you were refering to it being a maximum of 1m based on your grow room, in which case ignore this point, although it is true none the less)