I think that 7500 will be a good deal ... 16 pipelines with 350Mhz + better shaders and less heat ...
12x450 --> 5.4Gpx/s
16x350 --> 5.6Gpx/s (Good balance performance/heat i think)
16x375 --> 6Gpx/s
16x400 --> 6.4Gpx/s
You can see that with 350Mhz core frequency and 16 pipeline, this card will achieve performance of ultra (and better i think)
With 400Mhz (i think that a 9860 can handle it) it's very powerfull, and with 450 --> 7.2Gpx/s !!!! Or maybe...