A few sites charge more, most sites won't though, if you are in Scotland this tent fits the caravan and camping sites size spec and they have loads of sites up there (have a look at their website).
the only other size implication really is the bag size and weight, if thats OK then go for big.
Porches are fab but check the design- detachable ones like this are useful in that they can be removed quickly in windy consditions (open porches can be a wind risk) and and you have trhe option of detaching to fit smaller pictch sizes- this tent in only 3.5m wide without the porch. However on our old Tahoma (have you looked at them? new on ebay same price would also highly recommend and perfect for you as well, 190cm high) we found the enclosed porch invaluable for storage space- space always needs to be found one way or the other.
If you need a tall rent then you are going to get a big one- got my Mum one for Christmas and she can't bend due to serious pelvis problems, so had to be full height. We got her a gelert satellite 6- this would also work for you.
Hang on:
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satellite (apparently the satellite is cheaper elsewhere, not sure- got Mums as a one off somewhere)
now this is lovely, same ish price and would suit
Personally I think the Ontario or any of these would suit, the other choice perhaps- same site I linked to the Ontario- Gelert vario, another tall reliable tent.
HTH!