To answer your question simply: Yes. Keep T10. Resist the temptation.
If you are doing 10 man ICC heroic with your own guild, then you can just get a few pieces of offset gear and then try them out on target dummies. If these offset gears give better dps than t10 4pc bonus then by all means switch out the T10 pieces.
It's a guild 10man run, so loot rules can be more lax. I can understand using loot rules such as EPGP or DKP on 25mans...but on 10mans not many guilds use them, especially if it's the same 10 people going every week.