That looks like a narrow spring sniper spring, not an AEG spring, so would not fit.
You say your FPS dropped when you fitted an R hop. Did you chrono with 0.2s to get that FPS? Most R hop setups need to use heavier ammo to get the most out of them, so you will lose FPS anyway with the heavier ammo. I think I had about an M150 in my SVD and that was putting out 480 using a 6.01 inner barrel (on 0.2s) and twin point hop rubber, set up for using 0.3s in game.