buckslayer
First of all, good job for taking smart shots. You know your limits and that is the most important thing.
Drift hunting is a fun way to hunt it is just hard to get real close.
The 3.5" barrel is a good idea ,but they sure give a good kick on the H&R's. I am a firm believer in using maximum loads. Most people think this is nuts, but I like the extra punch of a bigger shell. Heck, I waterfowl hunt mostly with a 10 gauge and rarely lose cripples.
I would not suggest using Hevi through a full choke. I have read that it can cause barrel damage. I would suggest spending a little $$ and buying a box of Hevi to try out. It may make a believer out of you, it did me.
One suggestion I have is try sneaking up from the land instead of the water, it might help.
Sorry, I am not much help on this one.
Good luck.
