I spoke to an Irish guy on the phone this morning. I'd not managed to even start to focus on his name at the beginning of the call, before he'd gone on to give me his company, the quote number and 3 questions about the product codes. That was the first second of the conversation over in a blur of incomprehensible speed.
After about a minute, I'd managed to figuretively jump on him, wrestle him to the ground and wring a few words out of him. And conversation could begin. I found that the trick was to keep asking questions. He seemed to have an accelaration period, so the first ten words were audible. After which, he'd approached sufficiently closely to the speed of light for him to be inaudible in my time-packet.
I'm pretty good at accents. I was the only one of my friends who could understand Pat the glaswegian welder. Until he got excited or drunk, when only dogs could hear him.
I'd expect to get 98% of a high-strength SW Irish accent at normal speed. But like the tortoise who got mugged by 4 snails, it all just happened too fast...
I'm a bit of an accent mongrel myself. My parents are South London, moved to a South East market town, so add a bit of twang (burr?) of the old, dying, county accent and a large dose of posh, picked up from grammar school in the posher town-next-door. So it all tends to be a bit variable.