5 psi is a stock pulley on the TRD unit. When other 1gr's with the TRD unit want to improve, they go with a 2.85 pulley or a 2.7 pulley but if they go that route they'll need a 7th injector or 668 injectors (some run e85 as well!) and machine the snout. There is also a overdrive kit as well. Tuning is crucial here though, but I'm sure you know that. 10-12 psi is the limit on stock internals from what I have seen and I have seen some drop the compression to 9.5-9.6 running 15-17 lbs of boost. Some have also snakebitten the TRD unit with good results. Gadget just got one of his 1GR blocks sleeved with a closed deck and going to run a -91 blower!! That'll be F-ing awesome. APR right now is also working on a compound boost setup as well.
edit- And yes I still have my race spec N/A 1GR-FE fantasy.