Move up from Maximus 2.2 to 8.5, Difficult?

I've had my HTC one X running on Maximus v2.2 for the last while with no problems really.

Tried to install 8.5 tonight and I didn't really get it working, phone just continues to boot loops I just about (thank god) got the phone back working on 2.2 and all is well.

From reading it seems you need to upgrade the hboot on the phone.

Currently the phones bootloader is unlocked and running hboot .94.

Is it difficult to upgrade the hboot? I've tried and when I load the phone into "rebootRUU" mode it just won't load the firmware zip....

So I have two questions really, what am I doing wrong? and If moving up hboot is going to risk bricking the phone what is the highest maximus version I can go to on .94?

I've tried searching around xda-devs but really that site is a mess.

Thanks