Agree with all above. Not sure obout those plugs though. I would go for NGK B7ES or better still Bosch super 4.
Ed.. be careful with plugs. The scope for disaster is monumentally high.
NGK plugs are numbered with the higher number signifying a harder/"colder" plug. This is the other way round to Champion for instance.
If you had a super-tuned engine running on Nitro-methane and making 500bhp, you would probably have a "9" NGK plug in there. If you only ran to the shops and back, you would use a "5"... so your plug is at the "hot" end already (i.e. for a sustained rpm running/racing engine it's biggest problem is that it is likely to over-heat).
The standard NGK numbers for road cars are 6 or 7... so your plugs are not causing your particular problem. I'd speculate that someone put the "6" in there to try and cure the issues you're having. If the car is fouling plugs then a hotter plug (a plug with a lower number in NGK speak) is theoretically better at burning the soot off. A "6" is what you'd put in there if you had your problem and found that a "7" plug was fitted.
I think you're fouling plugs because you're over-fuelling it. Either your injectors are worn or your map needs a look at. I'd try a standard map and new plugs to start with. Until you solve the problem, another set of BCPR6ET will be cool... or hotter actually. Do you see what I did there?
You may be able to use BCPR7ET later.. (hotter runng i.e. colder plugs) when the beast is running properly... but one thing at a time.
Note that you need a projecting nose electrode by the sound of it
.. (the "P" part of the NGK code). Make sure you use these if they're what the car needs.. otherwise your spark is taking place too close to the top of the combustion chamber and that won't help.
fit projecting nose electrode plugs into an engine not designed for them.. they project further into the cylinder.. so your pistons have to be designed for the plugs to be jutting out. Obviously immense metal-carnage awaits if the piston is expecting a normal plug.
If you want to use 98-RON later too... then you can get a remap from someone who knoes what they're doing but anyway I'd revert to standard setup first and get the beast running properly.
Note that Bosch Super-4 (and the standard Golden Lodge plugs) are not hugely improved from a standard single-electrode plug. All that happens is that the spark jumps to the nearest electrode.. you sadly don't get 4 simultaneous sparks all happening at once, regardless of what the packet shows you. It helps the plug find a spark because there's 4 electrodes to choose from... but if your car was running right, you wouldn't really notice a difference with multi-electrode plugs on a race engine.