My Blob WRX currently has Milltek 3" decat, remapped, with a Walbro fuel pump.
Got a VF35 and STI pinks to fit together with K&N panel filter.
What are the benefits of decatting the up pipe at this stage of tune? Been looking at the Hayward and Scott one. Anyone any experience or recommendations?

 

If you want the best set up then have a word with harvey on here he does custom uppipes that help spool, failing that cheapest good option is a used newage sti or a classic uppipe, I believe removing the uppipe cat helps spool up and removes the risk of it breaking up at higher boost and going into the turbo.

 

yep, deffo worth decating up pipe, you get quicker spool and remove the exhaust gas temp sensor which is good at breaking up and going through your turbo, mine did this and luckily didnt cause any damage. For less than 400bhp a standard sti up pipe is as good as any other you can buy.

 

I've got my eyes on a few of classics which don't have cats in apparently.

 

While I agree with what you are saying generally I have to disagree with your last sentance, very strongly.
The Sti uppipe with no cat is a step forward from the WRX uppipe with a CAT, however it is only a partial solution. There are signifigant gains to be had, over the O/E STi item, even on a standard WRX below 220bhp using one of my stainless steel, purpose designed, slip jointed uppipes with five new studs and DEI heat wrapped, all for £139.