Or call someone who knows.
I always use MCT in Stowmarket, but there are a number of good Ohlins dealers out there, all of whom can advise you on the shock / spring and setup.
I know MCT have done a large number of GS's with both Wilburs and Ohlins and one of the guys there has owned a few GS's over the years.
My Tenere is going there in August for a Wilburs - which I had on my GS as well, have you also considered one of these?
IMO pretty damn close to Ohlins quality for a lot less money - and with a 5 year warranty, and each one is built to order, they ask your weight and passenger weight (if you hav one) as well as how often you ride one up / two up etc. and then build a shock with spring and damping to suit you and the riding you do.
Ohlins can also be tailored, but come as a stock unit and you then need to get them re-sprung / revalved if the stock setup is not right - although some Ohlins dealers may do this as part of a deal.