I measured the difference in size between the stock turbo and the 2530 and its like 2mm here and a couple there, bugger all really. The wastegate is much bigger though. The inlet neck is also better designed but overall, very little. I wasnt impressed.
Performance wise, the 2530 eats the stocky for breaky. It has so much midrange you can think you can take anyone on. Top end it falls over because its too small. My max power is at 5600rpm, after that you draw a straight horizontal line.
I would love to try something bigger, but i want a bolt on, something i dont have to piss fart around with dumps and inlets etc.