Well size is always hard to estimate,most sizes quoted are for approx 10years growth but obviously a lot depends on how the plant is grown.However I have seen photos of very large 'Tsuma Beni' and it does appear to grow wider than tall with age.I guess you've already looked at 'Tsuma Gaki' which I assume has similar growth habits.If it's just the springtime 'red fingernail' look you're after,perhaps research 'Satsuki Beni'.It produces the red tips on the leaves but not for very long.Maybe as this cultivar has amoneum leaves it might be more upright and vigorous but mine is far too young to tell.

Hi Jem! Thanks a lot for your reply, Satsuki Beni seems just perfect for me, unfortunately I can't get it anywhere here in Austria or Germany. Do you know a site on the internet where I can get a Satsuki Beni?

That's OK,I must admit I've only bought online once,from an english nursery(just 1year grafts).However we import a vast number of our maples from Holland.There are many nurseries there specialising in maples,Esveld & Dick Van der maat are the best known(http://www.esveld.nl/)(http://www.dvandermaat.com/)I'm sure Guy Maillot in France will stock it also(http://www.maillot-erable.com/)
Good luck with your searching :)

Looking and reading at Maillot-Erable I don't know anymore which one to get, this is really overwhelming!! Wow, thanks a lot!