I just downloaded the Mod Sotha Sil Expanded because it looks really good, but i have a question. I already have GDR installed so can i use the GDR Masterfile from GDR, or do i have to use the GDR Masterfile that comes with SSE?

Very good question. Checking them in TESPCD shows only one difference but checking them in WinMerge (a diff tool) shows quite a bit of difference between the two). Enchanted Editor shows the same number of records for each ESM.

The TESPCD entry is for the Dwarven Warhammer, GDR has the mesh as GDR\GDR_dwrv_w_warhammer.nif and SSE as GDR\GDR_w_dwrv_warhammer.nif

Looking at the NIFs in the SSE archive it should be GDR\GDR_dwrv_w_warhammer.nif

But then I'm not sure if that weapon's used by either mod. Hrm.

I'm afraid I can't help more than that. The two files are clearly different but are the differences material enought to affect the play of one mod or the other? I don't know. Trainwiz is still around so maybe he'll see this.