Going clipless and which shoes?

I don't agree with this last bit, and I hear loads of people saying size up with sidis they run really small etc -cycling shoes are supposed to be tight. I wear a 10 in street shoes ( Crockett and Jones or Converse) I wear a 44.5 in Sidis and these fit like they should, a snug fit with almost no toe room.
Trying shoes on when your feet are swollen from a days walking riding whatever is definitely good advice

http://www2.bsn.de/cycling/shoe-sizing.html

*Cycling shoes must be stiff, fit snugly and offer good support. One should not purchase too-small a set of shoes. If one or more toes make contract with the toe-cap when full-weight is applied toe-down then the shoe is too small. Up-until a few years ago, when shoes were made completely of thin perforated leather, it was not uncommon to purchase shoes 1 size or so too small, soak them in bathwater and let them strech to the correct snug fit. This legendary trick has, however, become obsolete by the newer (vastly superior) shoe generation and their use of modern materials. Good shoes feature very stiff and lightweight composite soles (often carbon) and sophisticated designs with natural (often specially treated leather) or synthetic uppers. The uppers are constructed to meet the demands of clipless automatic pedals: so a cart of mules could not pull it off!. Shoes should be purchased to fit at time of purchase. Unfortunately cycling shoes are, generally, not available in different widths [ed: Cycling shoes are a niche market. The concept of proper fit is on the decline in the entire shoe industry. In the hey-day of the New England cottage men's shoe industry a wide range of sizes and widths (some offering even two or more width measurements) where available in an assortment of derby, oxford and monk forms. Men apparently felt left-out from fashion and the market demanded trendy, poor-fitting, light weight, thin soled cheap imports. The trend since the 70s has continued and has taken with it several well-known companies. To become competitive even many well known international bootmakers (eg. Swiss Bally) reduced in the 80s the range of their available widths. New England's Alden, despite their use of 2 distinct width per shoe are typically sold in only a small range of widths. In Germany most shoe stores (including the up-market shops with $400 half-shoes) don't carry much other than a w-i-d-e width! There are, fortunately, a few rare exceptions but the message is that shoes with different widths are on the decline.]. The width should be snug but not tight. Too much sloppiness can effect knee stability and possibly affect the leg muscles due to over-compensation. A too small, or narrow shoe can effect circulation and produce pain and numbness. One should keep in mind, when trying shoes on, that ones feet can tend to slightly swell while in the saddle.

The only way to find correct shoes is by trial-and-error. While one maker might be too narrow another might be too wide. In general, the American/Taiwan/Korean shoes tend to be average to wide and the French and Italian shoes are average to narrow width.

The trend over the last decade is for shoes to be made wider. Since most newer shoes deploy a removeable insole [ed: often being produced in the same Asian factory alongside other U.S. and European branded mass market athletic shoes], sometimes "glued" in, a (very) slightly wider shoe can be compensated with an alternative, perhaps custom thermoplast, insole; but too narrow shoes just won't fit.

Despite a unified shoe-size measure, ones size can vary as much as 1 or more units from maker to maker, model to model and even production run. The number on the shoe is not the guide but the fit! The only way is to try the shoes on in a well sorted shop--- and don't forget to wear your favorite cycling socks.*