I wouldn't have any answer, had I not visited places like Adrian's Rojak Pot, and the Tom's Hardware VGA roundup articles.
Your 9600 was never quite mid-level, falling between basic budget stuff and the 9600 Pro that represented an excellent bang for the buck compromise for its day, in the lower one-third of the mid-level range. A 9500 Pro is faster than a 9600 Pro, and a 9700 Pro was the apex of Radeon cards for awhile. A far newer Geforce 6200, in 128 Bit form, is in about the same speed class as the 9600's, but adds SM 3, and more game system features, so it's technically superior.
The Radeon 9500 Pro is the least speedy card that ATI proposed as adequate for Oblivion, unlike the hugely exaggerated claims suggested by nVidia.
Only the top two FX cards ever were in the same general class as the Radeon 9500 and 9700, but they had SM 2 problems (which accounts for some Oblivion gaming tweaks that are needed). The FX 5900 Ultra and 5950 Ultra were pretty fast, but had to slow down to deal with SM 2. I have a 5900, not the Ultra. A vanilla 5900 or Ultra 5700 would probably not be objectionable in Oblivion, but really don't have a large speed margin (until a scene include SM 2, which your card covers without slowing down), over the Radeon 9600's.
No other GPU maker has been competitive in 3D since nVidia bought out 3dFX, just ATI and nVidia. But both tend to litter the landscape with sub-model letter groupings like LE, SE, GS, GT, Pro, Ultra, XL, XT, and I probably left some out. Avoid any LE's or SE's as a general rule (there may be some few specific exceptions, but in general these are low value for the price cards). Be careful of XT's from nVidia, since rather than a "plus" version, like ATI uses XT for, it is likely to be almost an LE, crippled version, instead.
In today's market, the vanilla Geforce 6600 has been roughly the equivalent of your old card, neither bare bottom budget, nor quite mid-level. The newest NV member of the class is the 7600. The 6600GT held the spot in the middle of the middle class for biggest bang for the buck for a rather long time, and is still a decent card. ATI left a longer time gap than usual between their last Radeon 9xxx's and their initial X-series, giving nVidia's Geforce 6xxx's a pretty open field to establish themselves in.
The Radeon 9800's were good cards, but lacked some features found in the newer Geforce cards, like SM 3. I will be using a 9800 XT to play Oblivion when my spare PC is ready to go. When it's in an ATI card's name, the XT's are better than the Pro's. The nVidia letter codes put GT's in between the Vanilla cards, and the Ultra models on the top, speedwise. Incidentally, even the X800 and X850 lack the full panoply of gaming goodies that nVidia was offering, although they did catch up in speed. It took the ATI's X-1xxx's to surpass the Geforce 6xxx's, but before those were out, the Geforce 7xxx's had started to appear.
These have been interesting times the past three years, for 3D GPU's, at least.
Off the top of my head, subject to confirmation, starting with the 128-Bit Geforce 6200 as the least capable card anyone has that will more or less play Oblivion, then comes the FX 5900 Vanilla, the Geforce 7300, followed by the X700 Pro, and then the Radeon 9500 Pro, and the 5900 Ultra, 5950 Ultra, Radeon 9700 Pro, Radeon 9800, Geforce 6600, Radeon X1600, Radeon 9800 Pro, Geforce 7600, Geforce 6600 GT, Radeon 9800 XT, Geforce 6800 Vanilla, X800, X800 GTO, X800 XL, and Geforce 6800 GS, X850 XT, 6800 GT, X1800, Geforce 7800 GT, X1800 XT, Geforce 7800 GTX, X1900 XT. The Geforce 7900's are a bit new to be sure about, I think the fastest is in the X1900 XT's general speed territory.
[ 03-26-2006, 08:10 PM: Message edited by: The Kiwi ]