Yes, it was the rotor size. I went to O'Reilly today to get new rotors, and their computer supports the use of both size rotors in the SSEi. And the smaller ones can work, as I have used the smaller ones for the last 3 years.
Put the new rotors on along with new pads. Because AutoZone took in trade some old pads I purchased there in 2007 (and gave me back $6 in cash), total cost of ceramic pads and Wagner rotors was under $75.00.
Attached are pictures of the small and normal size rotors, smaller on top.
2001 Bonneville SSEi, 219,000 miles.
Whats in my driveway:
1998 Chevy S10 4x4 ZR2, 1999 Olds Bravada, 2001 Pontiac Bonneville SSEi, 2007 Ford F-350 regular cab 2WD, 2008 BMW 335i coupe (Wife'* replacement for her Bonneville). The Bonneville is my favorite of all the cars in the driveway.