Actually Flakmonkey said he used the SH5 diesel room to work on.
Either way, Flakmonkey's stuff defininitely looks better than SH5's in most repects. The greatness is in the extra detail, the things lying around, better textures etc.
The SH5 u-boat looks more impersonal and more basic.
This also makes the SH5 boat seem far more spacious. I could almost think that the SH5 interior is slightly larger in scale, which may be right, but the dramatic difference is cause by the larger FOV in SH5 (notice the angled vertical lines).
Awesome work by Flakmonkey, and I hope that his work can somehow be integrated into SH5!