If you're shooting 3.5 it may or may not be too much choke. I'm shooting a totally different gun but my gun was getting blown patterns with the .660 (315 in a 10" at 40yrds) .665 (408 in a 10" at 40yards) The .670 gave a nice pattern, (446 in a 10" at 40yrds) but I'm thinking .675 will be the optimal choke constriction for my set up. I'm shooting IC as well.
Beretta A391 Nitro 3.5 2 7/16 8x9