So you want to fly your IVP at 4000 gross. Good for you. The certified maximum gross of your airplane will make a difference. After the NTSB is done reconstructing the departure stall accident that introduced you and three comrades to Saint Peter they will either write "Pilot lost control" or they will write "Pilot lost control and his airplane was over gross".  In the second case, besides being dead, you could lose your license for 90 days.

During testing I flew my IV at 10% over the 3200 certified gross (3520) in order to see how it handled in "Alaska configuration" where 10 over is allowed. I didn't like it but it was controllable. Besides, in Idaho you have to pay a yearly registration fee that is the princely sum of a penny a pound.  Certifying my plane at 4000 would cost me an extra 8 bucks....A YEAR!!!

By itself, a number written on a piece of paper will neither kill you or save your sorry ass. If you write down 4000 pounds as a gross weight limit one must conclude that you INTEND to fly at that weight. If this is the case, please do not introduce yourself to me because I would rather hear of the death of an anonymous person than the death of someone I have met.

If you are going to pull a random gross weight out of your rectum, I would suggest 6380 pounds. That way, the old Lancair brochures that list a 2,900 Lb gross can be salvaged by changing the pounds to kilograms.

Sarcasm aside, when I hear of someone "shopping" for a gross weight it makes my skin crawl. There were lots of dead pilots that were needed to derive the rules for determining an airframes' maximum gross weight. Ignoring those rules diminishes the contribution of our lost brothers. Listen to the dead and, as Hamid recommends, fly smart - fly safe.

Regards
Brent Regan