If I looked it up correctly, the max input voltage on the 2465 is the same as the 1052E (400V). I also saw somewhere mention 300V RMS for the 1052E. I think it's said that there should be a 10x correlation between GSa/s and bandwidth, so even if I hack it to 100MHz it should be good, right? But who knows just how much of a fall-off there is around the extreme frequencies, in comparison with the 3dB standard. Or if it'll throw everything off whack.
Thanks, guys, I think I'll keep doing a bit more research.