It's time to replace the Shimano 600 rear derailleur on my old Nishiki road bike. I noticed that the Shimano Sora comes in two varieties, SS and Gs. It appears that the GS will handle a greater range of chain tension than the SS. Will the SS work with my (fairly typical) road gearing? The sprocket sizes front and rear look to have a greater difference between large and small than some of the road bikes I see, but not so great as on mountain bikes. The bike model is the Triathlon (or something like that), if that helps explain the gearing.