I've replaced;
Plugs (Bosh FR6DC), Wires (OE Spec bougiecords), Cap, Rotor, All fluids, Vacuum lines, Fuel filter and all the sensors reported to be faulty by the diagnostics port which now reads 1-1-1 (yay!)
I've now installed a gauge and MBC on my '94 850 t5. Boost is set to around 14-15 PSI as I have read that there isn't much to be had past that. I've also read that MBCs can be dangerous to the rods if the boost builds to quickly in low RPMs but there isn't any information on how much that is nor how I can prevent it from happening other than a tuned ECU. The MBC completely bypasses the TCV. I'm content with the power that it makes for now so I was wondering if this is a safe option to run for the foreseeable future and if there's anything that I've missed that's critical to not killing it. (I've also overhauled the brakes and put some sticky tires on it so hopefully killing myself isn't an issue)
A M4.4 ecu is definitely on the list of upgrades which I'll attempt to tune using the info on the M4.4 wikia, just not top priority atm.