Hi flow cats won't suffer as quickly, but they will suffer. Your exhaust will end up being richer, and unburned fuel causes a reaction with the catalyst (sp?) in the cat, and causes it to melt together, clogging the exhaust. This is accelerated because with no pump, you're not supplying the extra air into the cat, which supplies oxygen, and thus raises the temp. Cats don't do squat below 750 degrees. So, the combination of a richer exhaust and cooler running cats eventually equal a clogged exhaust. If you elect to do this, you need to remove your EGR valve as well, because the EGR cools the combustion chamber, and eventually the exhaust. You will need to be running as hot as you can. If you are sold on removing your pump, I strongly suggest that you use an off road exhaust without any cats. It's much easier, and gives you less to worry about.