from my point of view: all oils get same thincknes / viscosity the only difference between them is amount of load which needs to be put on engine to get to that viscosity
so any oil with index 40 will get same viscosity regardless if its 0w40, 5w40, 10w40, 15w40 but each one of them have different viscosity in cold condition

our car run low revs, max 5-6k, so dont need to get any oil with index higher than 40, for normal day-to-day driving even 40 sims bit high

now when it comes to part-synt or full-synt its down to user / driver, part-synt will last 3-5k miles when full-synt 5-7k - simple as that

so saying that full-synt oil is too much "water'ish" is completly bolox and person who says that got no clue what he's talking abt

its the other way round, running too "honey'ish" oil can make damage as when turning engine on in cold condition for first few minutes you driving on honey not a oil !! its similar to having dishwasher pipes covered inside with loads of fat and try to get good flow - non-do-able !!

many people say: higher the mileage higher first index of oil - so going full/part/mineral oil - why ?! did engine spec had change during time ?! i dont think so !!

now when it comes to manufactor specification and oils used by garages ... lets be honest, most of places got no clue, most of places go for what is cheap not what is good

need exsample?! here you go:
bought my wife a year ago Suzuki Swift 1.3 2008 with 19k on clock
as i dont see point in paying them for oil and filter change 120 pounds when filter + oil will cost me 40 pounds, rather do it myself
now judging they know what they doing i would say they use proper oil from proper company ... well they put 10w40 Shell HX7 ... claiming that it is full-synt oil
well ITS NOT !! not only you can get that oil for 20.00 gbp + 2.5gbp for fillter = 22.50gbp (110gbp save), did argue with them but then had a look and service plan (which i ask to print out for me) and on plan (which is only for there own use) say USE PART-SYNT oil - bunch of w******

im not saying that HX7 oil is crap - cos it aint, but if im paying for full-synt oil i want full-synt oil
also changing oil in december for me personaly its obvious that oil with 10w grade and the best choice
even if they dont want to spend too much on oils (which they buy in barels anyway) 5w30 part-synt oil would be 10x better choice

now another thing ... lets count how many different barrels of oil should be in every Mitsi garages
- Mitsi makes ard 4 different types of engine (petrol, pefrormance petrol, diesel, perfrormance diesel) so there should be 4 barrels of engine oil
- 2 different gear oils - another 2 barrels
- PAS oil - 1 barrel - or stock of containers
- AYC - 1 barrel - or stock of containers
- ATF - at least 2 barrels

so we should see ard 8-10 big barrels of fluids + loads of containers ... but how many are ?! 2-3max !!

so not everything which is shinning must be gold my friends !!