Upgrading your RAM will only improve the performance if the problem is with custom textures and you currently don't have enough RAM to prefetch all textures. Non-custom textures don't cause this kind of stuttering.
Also, please note that more RAM won't help with shader compilation. You said that "I realise that this issue is lessened the more one plays a game", which sounds a lot more like shader compilation than custom texture loading.
Also, please note that more RAM won't help with shader compilation. You said that "I realise that this issue is lessened the more one plays a game", which sounds a lot more like shader compilation than custom texture loading.