meh to rb20det all round..
JaFF: sounds perfectly normal.. One way you can reduce the spool up is to add an exhaust camgear (i noticed a fair change with this in), get cooler air in (shield pod, or air feed it), reduce rotational mass (flywheels, etc), also try reducing the backpressure of your exhaust system will probably help.. maybe a dump pipe or get it heat wrapped. Electronic Boost control also helped mine spool up a tiny bit quicker (or at least smoother).
I think the smoother and faster the engine revs to a certain point, the quicker the turbo will spool. There is probably proper physics there somewhere which somebody can explain.