Something I think you should also consider is the cost of replacement bulbs. For some PJs these can cost not too much more than £100 but for others, they can be ridiculously high.
People seem to like this Planar PD7010 but replacement bulbs are around £350!!
Most PJ's only have a very limited bulb warranty, so should the bulb go, you'll have a cool bill of £350 if you want to continue using this PJ!
If you're on a tight budget, then I think this is an important factor.
Also, as others have mentioned, consider how you will set the PJ up in your room. Cheap DLPs have very limited zoom (refer to screen size calculators as mentioned above) and also no lens shift.
Finally I would also try to take into account the resale value of the PJ. Again, an important factor will be the cost of the bulbs. I think PJ are notorious for losing value (because the technology evolves quite rapidly) but people on a budget should consider this.
In terms of which PJ to choose, the 'safe' option would be the Z5 since it's very good and is LCD so no rainbow effect. The HD65 is cheaper but you will see the rainbow effect which depending on how you perceive it, will be either no worse than LCD screen door effect, or bad enough to give you headaches.
Get a demo if possible!