06
The 06 speed is a hell of a marker, it will keep up with anything out there. You don't need to shell out on any up's as it is perfect as it is!
air consumption is less than half that of my QEV Ion.
Occasionally you may need an exhaust valve but that will normally be sorted as part of a service.
The 05 speed is probably a better buy as it uses the old Angel threads meaning masses of cheap barrel kits are available.
That said, I have a complete freak kit for an 06 which I never use £60 posted and pp'd
The Angels are bulkier and heavier than etek's ego's etc so take that into consideration when choosing, but they almost never let you down!
Low Pressure means you need a gas bottle with a low pressure pre-set reg 450psi as opposed to a high pressure bottle 850psi.
I think most of the newer markers can run LP now but the Angel must have an LP bottle otherwise you will have velocity issues.