waste of money?

i have an 02 LB7, im running a 4" turbo back, PPE economy on 120HP, and a PPE boost valve. That should be good for just under 450HP at the crank. I have read that shift kits like transgo or PPE can handle 450-500HP. If this is the most HP i will be running for a while would it be a good idea to just get a shift kit? Do they really hold the power or are they just going to prolong tranny damage? If i had the $$$$ id get the PPE stage V that holds 1000HP and 1500ftlbs but.....i dont have an extra $4000 I know the stock allison should be ok with the power BUT to be honest im scared of breaking it . I just wana play with it and not break it, or break the bank!