Torque is what pushes you back into the seat in a rapidly accelerating car.
BHP is the power the engine can achive for a moment, i.e. you might have 500bhp, but it's at 6000rpm.
It's also worth noting that brake horsepower is the figure you get without the loss in power caused by the...
I had a Unichip fitted to my Swift.
Click for the graph.
That was on a 1.3 with intake and exhaust mods. I supplied the unit, fitting and mapping was £280 @ TDI in Essex.
You should have an overall power figure to aim for...
The "Power Boost Valve" is just a flashy name for a fuel pressure regulator, they all work in the same way, no matter which brand you buy.
I have one fitted to the GT, but it was there when I bought it so I can't say how much of an effect it had.