Hi, Two years ago I was in the same place as you (similar size, similar age) and chose gamma knife. I've had complications from the gamma knife (a small percentage of us can get swelling of the AN, further compressing the brain stem and doing more permanent damage to the three nerves), but if I were faced with the same choice all over again, I would choose gamma knife again. It's a personal choice. I think surgery has more risks.
But to answer your question, we heard a lecture at our AN meeting by a neurosurgeon who said surgeons have been surveyed and reported that surgery post gamma knife was more difficult, but he said that this is a red herring. The issue is not whether surgery post gamma knife is more complicated, which the surgeons that I consulted also told me. The issue is: are the outcomes worse with surgery post gamma knife and, if I remember correctly, he said there has not been much research done on that topic. The neurosurgeon who spoke to us said he felt that the outcomes with post gamma knife surgery were not worse. His hospital has also done low dose second gamma knife radiations, where the first failed. I had not heard of this before. My hospital has not done repeat gamma knife,
Gamma knife has been used on over 1 million people so far for 25 years in the US. In Europe it has been used since 1967 when it was invented in Sweden by neurosurgeon Lars Leksell. There may be research from Europe about surgery post gamma knife on the internet.
Hope this helps.