What a good thread!
cpp: one suggestion - you should not wear "slim fit" just because you are lean and slender. I'm probably like you but as tailor I would say that slim things are for womens. You should just get normal to your size. Some slim fitting meanswear are really obsolete and would give the slim men a bad look.
"And to be honest, when you've worn skinnier suits for too long, even a normal "Classic" fit suit will look like a sack on you."
I don't agree with you on this point - there are always compromises and a good "half way" can be found on MTM suits without being too slim and tight fitting, with a good sculptureness of the body (don't like the sack fitting too).
Right, is difficult to find this "measure compromise" on ready made suits.