To Hyundaitech - oil question

I have adressed this question on many adresses, but never got a really good answer. My car is Elantra 1.6 liter, model 2003, with hydraulic valve lifters.
I would like to use fully sinthetic oil, but there is a catch. I live in Croatia, and for our climate (up to 36, sometimes 40 Celsius in summer), manual (and hyundaiwebtech) recomends 10W40 gradation oil, but fully sint. oils come only in gradation 5W40 or 5W50 (and other not relevant here). Diagram in the manual shows that 5W40 is good only up to 20 Celsius, and 10W40 goes to 40 and more. Is it true that semi-synt 10W40 is better for hot climate than full synt 5W40? and if so, can I use 5W50 instead (it is not mentioned at all in that diagram)? The reason for abandoning 10W oil is because there is quite lot of lifter tapping untill engine is warm, and I am hoping to improve that with synt oil.
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5W40 and 5W50 are weights that aren't typically used here in the U.S. Realistically, I think you should be able to use the 5W40 without a problem, but I also don't have good data to peruse. You could try to look around the web for other viscosity and usage charts.
40C is not very different from the warmer areas in the US climates, and many automakers specify 5W30 in all US vehicles. This is why I think you'd have little problem with 5W40.
I don't actually know enough about the synthetics and semisynthetics to speak on the differences between them (or regular motor oils).
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viscosity chart in my manual as on Hyundai webtech site, and yet different viscosity is used. Interesting! Anyway, thanks for the info!
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