I work for a Grammar School (The state kind) in a borough that has lots of Grammar schools. I have been here 10 years. I would disagree about the money - many grammar schools have lower funding because they have fewer pupil premium students and indeed, they don't get grants to help them up their standards in specific subjects. So financing can be a bit more difficult than for the Comps in poorer areas - However the pupils don't damage anything - you can come back to your tools a day later and they are still there. The boys are pleasant and polite, and generally interested when you explain what you are doing.
The technology is possibly simpler because the teaching tends to be more conventional - i.e. less ipads more very fast PCs with autocad and Photoshop on.
BUT - the requirement for reliability is much higher. For the school - exam results are very important and a single lesson lost is a problem. In order to achieve this level of reliability, you either have to go for very reliable PCs or have a spare in each suite.
Personally I think there is more pressure on the staff in a Grammar school and hence sometimes you can end up on the wrong end of someone else's temper but it all tends to calm down quickly.
I don't know about other areas - but most of the IT managers in this borough meet and we all help each other, and I am sure if you just rang any of them up they would be more than happy to talk to you.
Good luck.
PS what part of the country are you in.