Hello!
I bring some updates on the issue, hoping that you folks can shed some light.
I went full $$ and replaced the FIP. The pump comes from a 300tdi defender, and I've confirmed that it hasn't been fiddled with (stock pin, everything looks untouched).
So, as you can guess...the car runs the same. Slow, sluggish, and with very high EGT.
I've tested flooring it in second gear from around 2000rpm, EGT's will get to 600ºC before I reach 50km/h.
It revs very slowly, with little to no smoke under load. When revving it on neutral, there is more black smoke (not too much I think) and some white smoke on certain rpm bands and throttle position, which I think it's very odd.
I've also checked the rear sedimenter and it looks perfectly clean.
Attached you can check a video of the car revving and smoking at neutral. I repeat that under load there is almost no black smoke, only when coming from a stop. The car was fairly cold (I know, I know) I repeated the same when completely warmed up and looked like there was no white smoke. Smell was clearly diesel, there is no burnt oil.
Thanks!