Thanks for the replies.
I understand the effects on the image from push processing, and as I said, I have pushed HP5+ alot to 3200 and got results I liked, I just didn't realise that Tri-X had a much lower exposure latitude. So now it's more a case of damage control, and finding the best way to develop it, to make sure I get all the detail out of the shadows that I can, rather than using the wrong developer and making it any worse.
Xtol was mentioned, and the closest thing I have to Xtol is D-76. Generally I thought that having a very dilute developer gave less contrasty negatives, but someone advised me that I should use D-76 stock. What are peoples thoughts on this?
I definitely prefer Tri-X over HP5+, but for when shooting at iso400. I think from now on I'll use Tri-X, but always keeps a few rolls of HP5+ incase I want to shoot faster.