I find HP5 to be one of the most malleable films ever made. Ilford probably takes it for granted, which is why they probably don't go to great lengths discussing it. Sites like the Massive Dev Chart lists a wide range of combinations. I actually really like shooting it at ISO 1600 (pushing two stops), and developing it in undiluted D-76. This is my favourite shot at this film speed to date, for reference:

Twice Bitten, not shy

Ilford HP5 (4x5in), pushed to ISO 1600 in D-76, printed in the darkroom on 12x16in Ilford MG IV multigrade paper

My opinion: Precise timings and variances posted on internet websites are not all that useful, as it's unlikely that your circumstances and needs match that which is referred to. It's almost impossible to screw up an HP5 negative (especially through overexposure) so just go ahead and experiment. Experimenting in a format that doesn't come in little canisters enough to take 36 photographs on does make it easier, that's for sure.

P.S. There are no problems in shooting Ilford FP4 at ISO32, other than somewhat low contrast. When you bump this contrast up in printing, you get lots of grain. I much prefer to shoot Pan F at ISO32 instead, which is simply stunning in all aspects of image rendition to my eyes - here is an example (also a scanned print):


Have fun!