In reply to Taurig:
Taurig, why not branch out and try on a variety of shoes before making a purchase; you might find a pair other than the Simonds that will fit and feel better. After all the more you try on the better idea you have of what you are looking for and what the market offers.
If you visit a specialist outdoor retailer or climbing centre-based shop, will benefit from not only a increased range but also hopefully helpful and knowledgeable staff with a passion for climbing, to help aid your choice. If in London, visit Ellis Brigham, Snow + Rock and Cotswold, all in Covent Garden; but for the best range and advice try any of the shops in the Castle, Westway, Mile End and the Arch climbing centres.
As for models, here is a selection from reputable, specialist manufacturers, that should see you comfortably through to the intermediate grades and perhaps, beyond:
Scarpa - Helix/Thunder/Vantage
5.10 - Spire/Coyote(and VCS)/Stonelands
La Sportiva - Cliff/Mythos
Evolve Defy/Boreal Joker/Red Chili Sausilito
Though as most others have noted, fit is imperative - no dead space especially in the toes and heel, good support under the arch and instep; and try to match the shape of your foot to the correct shoe. The width of your foot is important, some shoes are lasted wide, some narrow; the Urbanrock website gives a breakdown of this per model but any good salesperson should be able to look at your feet and make immediate recommendations. Bananafingers and Rock+Run also provide an valuable online source of advice and reviews but you really do want to try shoes on in person before purchasing. If you are a woman, buy women's climbing shoes; the female foot is far slimmer (even wide female feet!), especially around the heel than the male's, and thus the lasts on which the shoes are designed take this into account.
However, just as good shoes suited to your grade do make climbing more effective, throughout the grades; the same if not more, can be said for better technique and a higher strength to weight ratio!
Good luck and have fun shopping!