I have a TD5 D2 so I can't comment on the water effect on a V8, however, I have been stopped in my tracks in wheel arch high water and it is not pleasant. Although I do have a snorkel, the reason was my MAF sensor wire was inadvertantly trapped over the corner of the air filter box when the filter was last replaced, thus leaving a small gap to suck water in. Thankfully the engine stopped (guessing the cold water hitting the MAF in turn told te ECU to turn things off) and a couple of hours later and a whole can of WD40, she was running again.
However, what I can tell you is that when sitting in the water half way up my door, the water came in and sat about 1/2 foot deep in all the foot wells Lost my CD stacker and had wet carpets and gear in the boot.

Since then, I have run some fly screen rubber through all the door seals up to window height. This makes a huge difference as I now get zero water in the doors when wading. I have not been halted in water since though but would hope the seals would hold up if I were to sit in water above the bottom of the door.

My advice is if you are considering doing water crossings, then set your car up for it. I.e. snorkel, door seals, tarp handy etc etc. No point risking it as ost in our club have risked it at some point and come a cropper only to have their day ruined......especially in a V8 if i'm correct.

Spend the dollars on preventative measures now rather than fixing inevitable problems and then the preventative costs for next time