For wav files I use Soundforge, but only for single files (I don't think it can do batch normalization), choosing a factor of 90% (which from a practical point of view is almost like 100%, but without the risk that something along the audio chain can clip). With Soundforge you can also undo what you have done if you don't like the result.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.