I am doubtful that there's a meaningful sound difference. Even if you have IRs that were actually shot at 96kHz (which is a big if, as it's very possible that IR makers work at 48kHz and upsample), what that means practical terms is you're increasing the bandwidth to include sonic information up to 48kHz. There's going to be very little sonic information from a guitar speaker above 10KHz, let alone above 20kHz... IR processing is a linear function, so things like improved aliasing performance, which can benefit from higher sampling rates, don't come into play.