I have a 0.63 A/R turbine housing. Honestly I haven't driven enough turbo cars to comment on the responsiveness of the two sizes but this turbo doesn't appear to be unreasonably laggy. Testimonials and associated turbo setups added to this thread could help others decide on a turbo size but I'm sure the information is already out there.
But good to hear about the clutch setup! I'll keep that in mind if I start having similar issues but both my master and slave are only around a year old.
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