Hi Jay,
Yes I have tried the all-rubber strap on my 322401 and it fits perfectly and feels good - it mentally feels good too knowing I can contact water and not worry about the calfskin splitting from the rubber base, which has happened since I have gone swimming, diving, showering, even the sauna, etc with my watch, so maybe I'm asking for it. Like you, I'm tempted to use my watch for more than just telling time, although I probably should treat the case a little more like a baby.
The two main reasons I didn't get the strap are:
a) it's really expensive for two pieces of rubber, though I'm sure it's very durable and as you stated, it is way more rugged in the sense that it is just one piece.
b) in combination with (a), it just did not look good attached to the 322401, probably a combination of the patterned CF body clashing with the sleek all-black-matte no pattern finish. The original strap matches and enhances the look of the overall watch perfectly.
But I think it will look great with your 3225 since it might seamlessly blend into the case. The main issue with the look of the strap that doesn't match the sleekness of the 3225 and 322401 (IMO) are the ridges that stick out of the middle of the band, which does make it look more rugged.
You could just ask your local agent if he can remove the straps of a 3865 (if he has one there) and slip them onto your watch. Much faster this way than ordering a strap and waiting for it to arrive. I went into a boutique and asked and they let me try it this way.
I posted some pics of my watch after I bought it here: www.iwc.com/forum/en/discussion/64681/?page=1#post_497705
Some pictures of it at an F1 race day event:
www.iwc.com/forum/en/discussion/67029/
Congrats on your recent purchase! Take some pictures and if you do try/buy the 3865 strap, post those too! Hope your watch accompanies you and writes lots of stories with you!