I do encounter some slight stutters when:
surfacing
using binoculars
using free view
but not so much that they 'kill the joy'...
I thought my rig is pretty decent:
Intel core 2 duo 6400
2048 MB ram
Nvidia 7900 GS 256 PCX
I only play at 1024x768 and AA turned off
,
maybe some help can be found here, although is doesn't specifically deal with a patched SH IV
http://www.subsim.com/radioroom/showthread.php?t=108291