first of all that shop doesnt know what the **** they are talking about

the ITR has 10.6:1 compression and you can put down about 10psi on the stock internals safely

my friend has been running 10 psi..... 295whp/190 wtq for over 3 years on stock internals with no problems at all

if you go over 300 whp, or 10psi i would upgrade the pistons, rods, get a block guard and get serious tuning

but 5psi is nothing, you can easily put down 7-8psi if you are worried about 10

the shop probably is just worried because they havent tried it or something

but seriously, im not messin with you, you can run 10psi all day, just dont be stupid and go higher than that

unless your turbine is like a t67 or something huge, up the boost