before i get flamed i did try and search here and Google, but can't find enough specific answers and getting nowhere... Manuel says 5w30, but from my findings, 10w for a higher mileage car

1998 wrx
used as daily, basic mild mods, driven moderately.
175000 km on the clock

for my budget, deciding between two oils and will get one based on opinions best suited for me...

5w30 Castrol Edge fully synthetic ($50)
10w40 Nulon fully synthetic ($60)

so is 5w30 fine as that's what Ive always used or change to 10w40?

thank you