My $.02:
Metal Table:
I flipped a Gen4 performer earlier this year. Even though the prior owner said it spent its life covered, there was rust bubbling beneath the surface of the metal table.
"Upgraded" Ash Pan:
I'm torn on this one. I have this on my SSP. I like the look (mine has the black ash bucket), and the size/shape of the ash bucket. Initially, I wasn't a fan of the squeeze-handle bucket removal system. Now I don't mind the squeeze-handle, but I still prefer the older twist-style system.
Upgraded Lid Bale:
This is a wonderful upgrade, and one you can do a la carte. Weber Part No. 65188.
GBS Grates:
The Ivory Master Touch that I transplanted into my SSP frame came with the GBS grates. On the plus side, they seem well made and are substantially beefier (and heavier) than the standard grates. Now for the downsides . . . I don't use a vortex, and I can't think of any good reason why I'd want the center of my cooking grate to be removable. The gap between the center and outer pieces is a pain when placing food on the grate. I have to hold the center piece down to keep it from falling out when brushing the grates clean after a cook. I have to hang the main grate and the center piece separately when lighting the grill. I'm already considering going back to the standard grate, but I may look into modifying the GBS grate to make the center piece non-removable.
P-Shaped Bowl Vents:
One additional plus of the C&B performer is that the bowl should have the new P-shaped bowl vents. I'm still experimenting with these on my Ivory, but at least in theory they should provide better air flow control for low and slow cooks.
While you could order the lid bale, table, GBS grates and ash catcher individually, the only way to get Slate Blue is to buy Slate Blue. If it were me, I'd be more inclined to find a Slate Blue stand-alone kettle and modify it to work in the Performer frame. There's one for sale by me now, but the asking price is $200 and I just finished installing an Ivory Master Touch in my SSP frame . . .
Good luck. There are no wrong choices here.