Just being honest. By roasting darker *by roasting longer or hotter, or both* you're burning away the flavour compounds, caramelising the natural sugars and also releasing the oils to be exposed to the air - when then start going sour rapidly.
The biggest reason this seems to be done is to impart roasting flavours rather than using the natural flavour in the coffee - covering any flaws or unwanted flavours in the coffee, or to conceal the bean quality. I'd rather have a coffee that has been roasted to where it is best, than to a predefined brew method.
Weirdly, Starbucks actually buy some really very good beans, this very much surprised me. Unfortunately then then roast them to death to get a consistent 'Starbucks' flavour rather than using the beans own strengths.
Some coffee's as suitable for espresso and other's aren't. I've got a couple of naturals at the moment that I really don't get on with as espresso or brewed *using this term, even though espresso is a brewing method and it does annoy me* but add milk to them and they become pretty tasty. I've also got a bean that is one of the most lemony espressos ever - it's just an acidic nightmare, but is superb as brewed and in a flat white.
I've got assorted beans from 6 different roasters *Intelligentsia, Hasbean, Square Mile, Tim Wendelboe, Drop Coffee and St Ali* in the flat and even the darkest roast that I currently have doesn't go anywhere near the light French roast, let alone the full french roast. Some of these are designed to be espresso blends.
Check out the info here for a bit of a visual guide on roasting. I feel there's a stage missing between the light french and full french/italian roast, but as they say, the difference in timing is 30 seconds.
http://www.sweetmarias.com/roasting-VisualGuideV2.php
Another place you could try to get some beans is Monmouth. Been a while since I've bought any of their beans, but they do usually have a couple of second crack roasted beans. I would recommend asking when the coffee was roasted though as they do leave them out in big boxes, exposed to air and sun so it deteriorates rapidly.