Fully synthetics are different then simple mineral oil.
They are less thick than mineral based oils and deliver better performance.
5w50 fully synthetic will be less thicker than 10w30 or 5w30 mineral based
Morover i have had not good experience with using 5w30 in 1.8 grande the oil barely lasted 3k kms on harsh usage.
After pouring 5w40 fully synthetic oil didnt even sweat after driving continously on 170-180kmph for 2.5 hours.