If your employer is willing to pay for you to take the GISP and you feel like preparing and sitting for it, go ahead and do it. Being someone who currently holds the GISP, I would not pay for it out of my own pocket. As others have stated the CISSP carries the weight in the industry and it will be a rarity that you would see GISP listed on a job posting over the CISSP. Nor do I feel you see any significant increase in salary by having the GISP. Not worth the investment with your personal funds to get it IMO. My employer covered the exam expenses to take it so I went ahead and took advantage of it. I pursued it to establish credentials with GIAC.I sat for the GISP about two weeks after sitting/passing the CISSP exam. I did not prepare an index and sat for it primarily relying on my prior study for the CISSP. I did take my SANS books along and referenced them a handful of times during the exam. Content the same, slightly different spin on the questions.The CISM and ISSMP are very similar and both focus on InfoSec Management. I passed both 4 days apart from one another and used the CISM material from ISACA to prepare for both.
So, the differences I have found between SANS/GIAC Training and exams is that the exam questions are usually text for text right out of the courseware.
ISC2 and CISSP, the exam questions tend to be Here is the question, here are the possible answers. Some, or all of the answers are correct. But you are supposed to pic THE MOST CORRECT ANSWER.
Do they address that in the GISP course? Did you do any of the SANS practice tests? Were they a good prep for the CISSP?