Visibly, you can only tell the difference between 3 and 4 bar regs if you look at the part numbers. I wouldn't bother with 4bar (even though the revo upgrade itself is free) unless you're willing to shell out for the SPS3 controller, with that you can turn the boost down to practically stock performance. They'd have to be really looking hard at the dealership to spot all this so I wouldn't worry -too- much about warranty & servicing etc..
Having said that, running all that extra boost isn't a great idea without better cooling.. freeing up some back pressure on the turbo with the larger downpipe, CAT and exhaust would be highly advisable.
So yeah you could get the 4bar software now, but having it set to high boost pressures may just soak in the heat making you no better off until you get the Milltek !
Chris.