No lift pump and no problems??

Sooo...many yrs ago I junked the block mounted lift pump off my 200tdi and fitted a 12v facet cube type pump under the seat box (110 with rear tank). It was quite noisey but once the engine was running the diesel clatter drowned it out . Yesterday it suddenly went really loud, so loud that pedestrians were stareing as I went past and the noise was pretty unbearable for me too.
Anywhoo, pulled over to investigate and everything is fine visually so I hit it with a spanner which made no difference.
So I pulled the fuse expecting the engine to die or not pull max revs but no, she runs fine even at motorway speeds.
I know the Bosch ve FIP have an internal pump of sorts but didn't think it would cope with my 110 rear tank setup?
Is this likely to strain the FIP if I just carry on running like this?

I'm guilty of having strong suspicions of a dodgy fuel pump and not doing anything about it, it's simply slipped down the jobs list.

It's been that way for 3 years and many many miles.

If I let the level in the fuel tank go low, it won't pull the fuel from the rear tank, but with enough fuel in (and therefor pressure) it draws fine.

Hmmm...my tank is full!
I've read so many posts pointing fingers at lift pumps for poor performance issues, lack of higher revs etc' so I am a little surprised .
I went around 10 miles at 65/70 mph no problems at all.

Yeah mine shifts along alright.

But I'm confident the pump isn't great as it wont pull that last bit of fuel when driving fast.

Dont forget the lift pumps have little poppet valves in them that will restrict the flow of fuel if its not working.
I have the same set up as you on a 90 with underseat tank, pump is on a switch and sometimes forget to switch it on but to be honest it doent make much if any difference, but must make life easier for the fip.
Brilliant for bleeding though
If you read the specs for the fip installation on the defender you will see that it will run fine without the extra pump, but its on the limit distance and height wise hence they fitted the mech lift pump.
I cant find the numbers, but this may help?

Fuel-line configuration

For the injection pump to function ef- ficiently it is necessary that its high- pressure stage is continually provided with pressurized fuel which is free of vapor bubbles. Normally, in the case of passenger cars and light commercial vehicles, the difference in height between the fuel tank and the fuel-injection equipment is negligible. Furthermore, the fuel lines are not too long and they have adequate internal diameters. As a result, the vane-type supply pump in the injection pump is powerful enough to draw the fuel out of the fuel tank and to build up sufficient pressure in the interior of the in- jection pump.

In those cases in which the difference in height between fuel tank and injection pump is excessive and (or) the fuel line between tank and pump is too long, a pre-supply pump must be installed. This overcomes the resistances in the fuel line and the fuel filter. Gravity-feed tanks are mainly used on stationary engines.