Although I am not very fond of HP5+ (just personal preference - no technical reasons), I have shot it at 400, souped in Rodinal 1:50 and especially in 120, the results were very pleasant. I don't think you will find the grain objectionable. I have pushed this combo one stop as well, and again, it responds fine as well. And I can tell you that the photo of Andy's cat at 3200 looks great - so its obviously a flexible combo.
I have shot APX400 and TriX in that speed mostly, but with the demise of APX, and my personal preference for spending my money on Ilfrod products, I think I may be using HP5+ more myself - perhaps I just never gave it the time to get what I wanted out of it since the other films were available and I liked them. I guess you could say it was more a matter of liking other films and not taking the time to really get to know HP5+ rather than any real objection to any of its qulaities... Hmmm.
I have rambled again - best of luck,
Peter.