That depends on several things. Do you ride with a passenger? With luggage? If you are very tall, you may put more weight over the rear wheel, and so on. I would fit the shocks to the bike, and measure suspension sag with you on the bike, in normal riding position. I guess the shocks should compress about 30% of their total travel, as a starting point. I have some suspension books at home, that I could have a closer look at, when I get home from overseas next week (Wilbers and Racetech suspension "bibles", and Tony Foales "Motorcycle Chassis Design")
You may need a buddy or two to help you measure sag. One to support the bike, and one to measure the c-c of the shocks. For checking sag on the fork, you can use a cable tie around one tube. If you want to be really scientific about it, take two measurements for the shocks and two for the fork. Have the second helper compress the suspension a bit extra, then ease off slowly, and measure. Then have him lift (extend) the suspension a bit, and ease off slowly, then take a second measurement. These two measurements will differ, due to friction (hystheresis). Actual sag is the average of the two.