The dealer should be your deciding factor, which is better for you in your area. The 8820 is a much larger machine than the 760. They are both very similar in design so servicing should be close to equal. The capacity that you are looking for and the dealer should answer the question.
The 760 and the 8820 are almost identical in capacity. I had a 1980 760 and my bud had a 1980 8820 and we were dead even at all times. The 8820 is turbo charged but I had a tuned V-8. Iprefer the 760 because it easier to work on in my opinion. Also the 860 was discontinued in 1987, a big shame I think.