most stock honda sleeves can handle up to 450-500, but the b20 are more prone to crack at lower power levels. i would say about 300 on the b20 to be safe at the most.

boost is a relative term because one turbo at 5psi is less than 5psi from another turbo. i've tuned b20 vtec turbo's to 280ish w/o sleeves cracking.