With an extension subject you have to take onboard that its like the work of a two unit or higher subject but its only worth one unit, then again, this one unit could be like the 'make or break' for your aim ATAR.
personally, i think if you find the pressure of extension english too hard- like content as well as the time it takes up (cause we all obv dont have enough hours in a day as year 12 students) then drop the extension.
On the flip side, physics, ive heard, is a huuuuuge workload and theres a lot more to it. when you think about it the exam - final exam, is a lot bigger
-english is only an essay and a creative
-physics is more.
there are positives and negatives to that, with english you'll rely on those two questions for marks where as in physics you can get them from elsewhere in the paper.
what i did when i was deciding what to drop (i was doing 15 units) was write down the benefits as well as the disadvantages of keeping each subject.
at the moment i have 14 cause i want to play out my subjects for longer rather than make a rash decision and drop one too soon. so yeah.
i hope that helped you ^_^
xx