Mate, with the big questions you can save heaps of time just by estimating SGRs -but it takes a bit of practise to estimate an SGR to the nearest decimal point. Work out some rules of thumb to adjust your SGR allowing for wind component, aircraft weight, abnormal configuration etc. MOST of the time, an estimate will put you close enough to the correct answer, but if you land between two answers, you can still do the full working without having lost much time.
Try combining sectors as well. Take your three (or however many) sector forecasts, weight them according to distance, and make up one average forecast to cover the whole route.
Bit tricky, but it when you do your practice questions it takes very little time to estimate a wind vector average and an SGR, then see how close you are after you work it out fully.
It worked for me anyway. I got all the big questions correct and had plenty of time to spare.