my 0.02.. i think the 5 zip nearly always works better in calf, it suits the drape of the jacket better (drew said the same thing once). it doesn't look bad at all but i would encourage you to try a size down and see if you can achieve a cleaner fit in the chest. (depends whether you plan to wear it zipped or unzipped.. i hardly ever zip mine). in the end though, it's a very versatile pattern. a friend who is a full size smaller than me has worn my 5 zip and it looks...
stanley, i would second parker's suggestion to look out for kilgour RTW suits from the carlo brandelli era, they can often be found on uk ebay. clean, structured shoulder, longer line coat and a slight taper to the trousers. very much that combination of formal with louche that you seem to be going for, and can be had for relatively cheap
only tried the natural linen but it looked fine sized down one. mbaum said he could've sized down also. you should be ok, particularly if you plan to wear it open most of the time (which i think looks best anyway)
if you are heading east, hostem on redchurch street is my favourite store in london:http://www.43hostem.co.uk/shopping/items.aspxnot far from there, tayyabs is a good call if you're into punjabi foodhttp://www.tayyabs.co.uk/(pm me if you need any more recs)