i worked in 3 different opticians over 11 years - the best one i worked in was a small independent optician were i stayed for 9 years - all the staff were trained to a very high level and everyone knew their stuff.
what i found when i left and worked at a large chain was that many staff were not trained well at all and were souped up "sales" assistants rather than optical assistants.
having said that most large chain opticians are franchises - even Boots opticians are mostly franchised. so are specsavers.
it really does depend on who runs them as to how good they are. my friend works in a small specsavers, he is a fully qualified dispensing optician and trains all the staff to a high level - the specsavers i worked in however was pants, and i knew more than their so called qualified staff because i was so well trained at the independent i worked in.
i still go back to the independent i used to work in - its more expensive but worth it as i know there will never be anything wrong with the test, the dispensing or the making of the glasses.
my DH has a very high prescription too - i feel your pain price wise! but i saw some real dispensing disasters at the pants specsavers i worked in so i wouldnt touch that particular branch with a barge pole....like i say though they are all franchised.
prices are usually cheaper at the big chains and they have offers on but for me i would rather stick to the indie i know, and pay more because i know exactly what im getting will be spot on, more so for DH who is a high prescription and is sensitive to changes in his lenses.
ask for recommendations locally, you may have a fantastic franchised big chain near to you - or if they have a fully qualified dispensing optician ask to have them measure you up for new specs and frame etc.
are you short or long sighted? having a high rx affects your frame choice quite a lot and any assistant or dispensing optician worth their salt should advise you honestly.