The only problem with the cap
The problem with the cap is that the cap needs to be higher for those with status.
I'd propose this to United (if they must have caps):
No status: 25k (Equivalent at $5k spend)
Silver: 50k ($7.1k)
Gold: 75k ($9.4k)
1k: 100k ($9.1k)
GS: Unlimited
That seems fair.