Engine Oil 05w-50

[GSSPORT]

Hi All,

I have a mark 2 GS300 Sport, I have had it for over 3 years and always used a fully synthetic 05w-40 oil, It has now 152k miles and I have had it since 88. I do alot of motoway mileage (about 99% - 1% in town). As such, I thought it may be better if I used a thicker fully syn. Halfords now do a 05w-50 fully syn (I have always used their 05w-40) as I do alot of motorway driving, I thought of swapping to the 05w-50 from 05w-40.

Will this be ok for my high mileage care or should I stay with a thinner 05w-40 synthetic or due to the mileage go for a semi-synthic if so which one????

Any advice greatly appreciated.

Thanks