Hee hee - I loathe people who say 'I told you so' - don't you?
I think you'll be gobsmacked at how quickly you achieve that 8.5 or at least, a darn good reduction in whatever it is you've got used to seeing - I sincerely hope you do anyway, since that's the whole purpose of the exercise.
All DVLA will do, is send you a licence you will have to renew every 3 years - however they will rescind your existing rights over and above 2500 kgs - the old C1 - and upwards but if you NEED more than a car licence, then there are ways of reinstating some of them. Keep a copy of your old licence if you've got eg a motorbike licence on top of your car one. You shouldn't lose that particular category - but they're a bit fond of accidentally missing things off and if you haven't still got your 'pink' slip it's the very devil to prove now that you passed your test for it in c.1969. One chap we heard of that this happened to was a flippin Police Motorbike instructor !!!
Main thing is, the testing rules - before driving every time (unless you only did it a short while before) and every 2 hours whilst driving. So either pull off the road somewhere safe whilst on your journey and do it, or say drive to client, do the business, come out and it's 100 minutes since the last test and next apt is 30 mins drive, do it there and then before resuming your journey again.
The knack is managing your diabetes to fit in with your life, whilst sticking to the Law and minimising the risk to your health. Always wanted to be a juggler, secretly, didn't you!!