Just a few notes, upgrading shocks isn't a bad idea, but it should be done with some goals in mind. What are you trying to accomplish by upgrading the suspension? Is your rear suspension correctly adjusted now? Upgrading the back without consideration of the front is only tackling half the problem. We can be of more help if you add more info.
If you change shock length from OEM you'll affect the steering geometry. Shorter will slow the steering as well as reduce shock travel limits. Longer shocks will speed up the steering (shortens trail measurement) increase ride height and add some travel. There's an upper limit to taller shocks usually about 1 inch eye to eye. I had 1 inch over Hagon Nitro's on my 05 Standard and put progressive fork springs in that were 10.5Nm/mm. That made for a very smooth ride, but it was taller to get into and out of the seat.