A drop from 121 to 75 is brilliant in only 3 months. No wonder the nurse was happy. Please don't be disappointed - it is an excellent drop. (and don't forget the HbA1c is a sort of average of the previous 2 to 3 months so will include the time you were stuck in the 9's.) Also well done to the nurse for saying statins versus diet and exercise are your choice.
As for your cholesterol of 5.4, this is your total cholesterol, and unless you know the breakdown this figure is fairly meaningless. You need to know the HDL, LDL and triglycerides which together make up the total. The HDL is the good cholesterol, the LDL is a bit of a mix, the triglycerides are the baddies. What you need is a print out of the blood results - not just for the HbA1c and cholesterol, but also the kidneys, liver and anything else they tested. A good tip is to never, ever, accept the words "fine" "good" "OK". The nurse and GPs ideas of what are fine may not be yours. You need the actual levels, particularly so you have something to compare when you have your next lot of tests in order to keep an eye on any future trends.
If you are in England your surgery should put blood test results on line. You do have to register for this through the surgery and complete a form. It saves all the hassle of waiting for results - they just appear on line. Mine are often there within 24 hours. In the meantime, print outs are available when you ask. The receptionist usually does this.