The impact of having your load-script divided on multiple tabs shouldn't be measurable.
I won't exchange an easy overview for assumably some picoseconds.
In the past I've had some very large load-scripts but performance-gaps were never through tabs but through inefficent loading-statements or joins.
There is not. Tabs are only visual aids to help you in the development process. The script is always run from the first line in the first tab on the left to the latest line in the latest tab on the right, sequently. Actually, if you either export the script or run in Debug mode you will see how there is a //$tab indicator with the name of the tab, but apart from that, all goes from top to down line by line.
Hope that helps.