Normal rate of rise for brake pressure? Soft/slowly sinking pedal

I have a 2003 Jetta wagon with manual transmission - without ESP.

I recently replaced front pads and rotors and ran the master cylinder dry during bleeding (manual bleeding). During the initial start, the brake pedal felt soft with the car running, but rock solid with the car not running. There are many threads on this subject and it seems like a majority conclude this is relatively normal for these cars, though I don't recall this before running the master cylinder dry.

I subsequently replaced the master cylinder with one made by Metelli along with new rubber front brake hoses. I bled the system with a Motive pressure bleeder this time and activated the ABS pump with VCDS. No change in pedal feel upon restarting the car. It stops well, but the pedal doesn't feel right. I can pump the pedal at slow speeds and the point in the pedal travel where it changes from firm to sinking will rise briefly, then just sink slowly to the floor as if I hadn't pumped the pedal.

I've read through the following thread about a failed brake booster resulting in a sinking brake pedal, but constant brake pressure:

http://forums.tdiclub.com/showthread.php?t=475407

Since I don't have ESP I don't have brake pressure available in VCDS, so I bought a brake pressure gauge kit to test before concluding I needed to replace the brake booster. The link below is a video of the rate of change of pressure.

https://www.youtube.com/watch?v=dhNZ4UmEs9M

I'm pressing the pedal quickly down to the point where resistance changes, then maintaining as close to a constant force as I can manage as the pedal slowly sinks to the floor. You can see the gauge quickly rises to about 50 kg/cm^2 (about 700 psi) - the point at which the slow sinking begins. Then the pressure slowly rises to about 130 kg/cm^2 (about 1850 psig) or higher, depending upon how hard I press the pedal as it reaches the end of travel.

Is this rate of brake pressure change normal? I've never measured brake pressure on a vehicle before tonight, so I don't have a comparison. I don't have any other TDIs to compare right now. I'm hoping that ESP cars are a reasonable comparison since I doubt that measuring brake pressure with test gauges is a routine task for most folks.

On the thread above, it reads like the pedal was actively being drawn towards the floor which is definitely not the case on my car. I still get one good (well, as good as it gets) brake application after I turn the engine off, so it looks like the vacuum side is tight. I have another video on my YouTube account showing pumping the pedal and the vacuum assist on a start several seconds after the engine is turned off.

If you ran the brakes dry when you were bleeding them, you might have some air in there. You will need to use a scanner capable of running the abs to bleed it until it runs without any bubbles. Use the sequence of rr, lr, rf, lr. The other thing to check is the tandem pump hose connection. The barb tend to work loose on the older versions of these. One minute you have brakes then you don't and back to good brakes. If you have a vacuum gauge, you should have 24-28 vacuum on your gauge. If not, start looking for a cracked hose, loose barb on the tandem pump or a bad hose going to the turbo.