Since I've already driven 6000miles with my old oil, I visited my local service to get some prices for oil, filters and stuff. They recommended me Total Quartz Racing 10W50. Have you ever used this one before? 

I'd recommend Mobil 1000 15w40, reasonable price and good oil. 

 

http://www.halfords.com/motoring/engine-oils-fluids/engine-oil/mobil-super-1000-x1-15w-40-oil-5l

I would think they are too thick.

 

Millers Oils recommend a 5W-40 (XF Longlife). Opie oils and Castrol recommends a 5W-30 (VW 504/507 spec) oil.

The MPI should have 10w/40 oil.

10-15 year old cars are fine on oil specs. from 10-15 years ago, surprise surprise, this modern fully synthetic guff is all well and good but the engine just doesn't NEED it or indeed benefit from it, only PD engines and turbodiesels are oil critical, N/A petrol engines really don't care as long as it's fresh and changed regularly because they don't soil and dilute the oil like diesels do. Use whatever is a good deal and stick to the intervals.