From your description I assume you passed a number of overhead gantries which displayed "60" and finally one which displayed "50" and it was this final one which flashed and resulted in enforcement.
This is not an average speed stretch. It is a variable speed limit motorway, and the variable speed is displayed on each gantry. You must not pass a gantry in excess of the speed displayed, regardless of what speed was displayed on the previous gantries.
I still plan on going to court and represent myself,
If my assumption above is correct, how do you intend to defend this charge in court? The police will probably produce a photograph of your car together with one of the speed displayed on the gantry, taken at the same time.
i think a jury would also agree eyesight on a speedometer needle is not the clearest
There will be no jury involved. Your trial will be judged either by a District Judge sitting alone or more probably by a Bench of three magistrates. If you cannot read your speed using your speedometer you should consider either getting your eyesight checked or having a replacement speedometer installed. Whatever is the cause of the problem, it will not provide a defence to the charge.
If you are convicted (and your speed was 65mph or less) you will pay a fine of half a week's net income, a surcharge of 40% of that fine and prosecution costs of around £650. You will also have three points imposed on your driving record. The court will make a "collection order" and if you do not pay as directed measures will be taken by the fines enforcement office to recover the sum from you. This may mean bailiffs visiting your address. If that is unsuccessful the matter will be returned to court and the court may make an order to have monies deducted from your earnings or benefits, as appropriate. If that is also unsuccessful, ultimately you can be sent to prison for non-payment.
I dont blame police, this is the council and highway maintenance trying to get every penny they can
Neither the council nor the highways authority have anything to do with this. Whilst the reduced limit is imposed by National Highways, they receive no benefit from it. Course fees are split between the course providers and the police; sums paid in fines, fixed penalties and surcharges go to the government's funds; prosecution costs go to the prosecuting authority.
Do let us know how it goes.