Scrog or not to scrog that is the question

Okay this is my first indoor grow and im trying to figure out wheter to scrog my plants or not. currently i have two white widow femized seeds vegging under 7 23 watt cfls. They currently stand at 7 inches tall. I plan to put an order in this week for a 450 watt hps. Now comes the height issure i have about 42 inches of usuable space give or take. should i introduce a screen and keep them under 2 feet tall or should i induce flowering as soon as i get my hps light. I could probabley handle a 2 1/2 footer. I'm just not sure how much there going to grow.

scrog is a nice way to go especially with your space limitations. get the screen and start training them now. if you keep them trained and the branches under the screen then you will only have buds above the screen. now if you get 42 inch tall buds then I applaud you