Can only comment from experience, as mentioned my friend has one, and on a short road he leaves me, but on a longer road I can pull in 4th, maybe its just the way his map his sat, as said its only from the one car i've seen.
The rumour around poping came from his tuner, he said once you go over 230hp the head gaskets go and the engine is at risk, as said rumour...
i have a friend who has one, since im getting one i wanted to compare..i will say the fiesta leaves the clio standing until you are in the rev band and start to clamber some meteres back..the low down torque is insane, plus when it gets onto over boost it gains all that extra power..they are as quick as each other but i would say the turbo will always be marginally quicker!
and i find that rumour very hard to believe since mountune have already talked about a stage 2 MR kit which would be intercooler, exhaust and map..which being stage 2 would likely see you between 230-240bhp i would imagine.