If all you're looking for is a better sear, look into getting some Grill Grates. Tommy (TMB) should be along to address the rest of your question in depth. Listen to what he says; no one knows more about the BGE & SRG.
Now your making me blush Turtle
The SRG is much better than the standard Big Easy in soooo many ways!
The unit is larger so you can cook two large chickens or butts if you wanted to, and even a bunch of ribs if you place them around the basket in a circle. Although you said you have left over chicken, this is major selling point for some folks because they need a compact cooker that can cook two birds or even butts at the same time
The SRG can also be used as a grill that can exceed 600 degrees, mine go over 700 but mine have been modified to cook the way I want them to cook. So searing a steak is no problem and if your into reverse searing it does a wonderful job.
The reason the Weber grate didn't work so good is the fact it's tube steel not the rib design of the SRG. You see infrared just passes through the tube style grate where the infrared is caught by the ribs and holds it so heat is transfered to the grate causing VERY high temps yet your food wont dry out like it does with a standard grill.
Infact, the new infrared/charcoal grill made by CharBroil uses the same basic grate for the same reason.
You could however add GrillGrate's to you Big Easy and have a nice little grill but the SRG with the lid works much better
Although you have a pizza grill, the SRG can make some really good frozen pizzas and by adding a pizza stone a fresh pizza should not be out of the question. I bought a Primo pizza stone so I can use my SRG as a pizza oven. I was told the Primo stone will take 600 + degrees. I hope they are right
The SRG does put out 18,000 BTU's and the Big Easy 16,000, but with the increase in chamber size you need the extra BTU's
I hope this helps,
Tommy (TMB)
