have a look at this for spool up time from wet bearing and ball bearing
http://www.jgstools.com/turbo/50vsgt40.jpg

i don't like ballbearing's they break easy i seen enought with snap shaft
a bit of spark plug coming off will damage the shaft and you wil need a new core
wear a old t3 you can replace the shaft which is cheaper

what a bout t28 from pulsar they the same as disco potato size