Tafka_steve...Whatever you think about the sonic characteristics of Shure cartridges (and other stuff) Shure does an outstanding job of testing and specification. I believe Shure specs. For the V15mr They say "esentially flat from 10 to 25KHz". The graph shows a dip of about -0.2 dB near 16KHz, and then a rise to about +0.2 dB at 20KHz (where the graph ends). The low end is completely flat to 10 Hz.
However, the RIAA curve is only defined from 20 to 20KHz, so phono preamp frequency response can really be talked about only in this range. Outside that range, say up to 100 KHz, a phono preamp can use whatever equalization is necessary for flat response. I said that 100KHz is a walk in the park for electronics. If that were not the case there would be no radios, much less radar or GPS.
My phono preamp is ancient: a PS Audio II. However it is a very simple circuit built with some very good components, and I have never felt the need to replace it. There are but two gain stages with a passive RIAA equalization network in between them. Open loop bandwidth (-3dB) is 120KHz. From 30 to 20KHz it's spec'd at 0.1 dB. There is a rumble filter that brings the response down -0.25 dB at 20 Hz. A "small" amount of negative feedback is applied "for stability and lowered distortion". With feedback the bandwidth is 1.7 MHz, but there is an RFI filter which brings this down to 550 KHz.
I really think that there are more important things than extended frequency response in a phono cartridge and/or preamp. I did like the sound of the MC cartridges which I used, but they didn't track like the Shure, and the Stylus replacement issue was an ongoing headache.