TO SCROG OR NOT?

The decision to scrog or not is based on what you want as results.

If you are looking for the most final weight of buds there is no question that scrog will beat any other method for a given floor space especially if you have limited height. You said you only have 42" of vertical room so this is one of the best reasons for the scrog method in your case. Pretty difficult to grow 36" plants and still have room for the grow medium and the lights.

I have grown scrog style for six years now and my current favorite method is to use T5HO flourecsent bulbs/fixtures at about 50 watts per square foot of grow screen. My current setup uses a 4' x 2' eight bulb fixture over a 4' x 2' sreen area. I keep the lights about 1" to 2" above the plants at all times. (must use fan blowing to cool)

The downside to scrog is the labor/time needed to train the plants under the screen and the learning curve needed for this method. This is a two edged sword in that it can be very beneficial for new growers to actually look at and touch the plants every day or so as this will speed up the learning curve and make it easier to catch problems early.

For me the final reason is that scrog method uses far fewer plants per square foot and gets much more production per individual plant. Some areas of the USA have legal restrictions as to the number of plants an individual is allowed to grow legally.

Low vertical height and the subsequent heat issues involved should be enough for you to choose scrog.

PS: for the 4' x 2' screen I have best results with just two plants per screen.
If you do not care about plant count and want less labor/time SOG may be for you
but you still have the vertical height problems.

hope this helped,
Max Blast