I do not remember which 4gig Patch that comes with Ralles Mod Pack, but I'll refer you to CapnScurvy's comprehensive posting of
Windows10; Large Address Aware; SH4 Install, especially since your build is right up that alley. I don't even have a tenth of the computer that you have, and Ralles Mod Pack runs very well on my Core Duo quad-core box, with half the ram and vid card... One big thing to remember about mods and Silent Hunter games, is that if you are using the Stock "Save" folder, you ~have~ to empty that "C:\Users \UserName \Documents \SH4" folder in order to clear any remnants of the previous game version. The only way around that is to use MultiSH4 and multiple copies of the game, to keep from "cross-contaminating" the game from the Save folder information.
Also, be sure that (if possible), your game's display resolution is set to match the Windows display resolution, which should be set to match the monitors "Native" resolution, which will show in Windows as "Recommended". If you happen to have a high-end monitor, you might not find the display resolution in Silent Hunter 4, in which case, you would choose an evenly divisible match, such as a 16:9 or 5:4 or whatever. If the video stream has to do floating point division to "draw" the game on your screen, that can really slow things down.