I'm told the WRX has less grunt down low. Other notables are that anyone with an STi who is going for power is replacing their cast pistons with forged.

The low-end grunt is down to AVCS, the variable cam timing voodoo that Subaru uses. I believe it's tunable with the right aftermarket ECU programming or what have you, but I am not certain.

If you read my woeful tale, there are some people who actually prefer the WRX motor.

Part of my struggle in deciding between using an STi or WRX short block was in understanding what the 818 would enjoy the most. Does it really need low end grunt? How much power is too much?

I think chasing big numbers at this point is a mistake. I think the smart move is to see how the initial builds sort themselves out on the autocross course/race track and then decide what the right power source should be.

As far as the suspension and brake bits - the front lower control arms on the Open House chassis were very different from mine. They looked to be fancy aluminum bits. You'd have to ask Dave/Jim where they came from - they might be STi bits, or they might be aftermarket, I don't know. There were a couple of other arms that I wasn't sure whether they were aftermarket or stock. Again, I think the smart money is on waiting to see how things build out.