So, at the moment I have two Weber filters under the bonnet. Need to cut a hole for colder air and better power, but should I change the filters too for more power?

Thanks
Ed

Foams method of filtraintion is usually better.
As long as it's a high quaility filter it won't make a noticable difference.

I'm using K&N's with 16mm trumpets inside, reccomended by a local weber specialist, on the dyno at worse they were .5bhp down on 60mm open trumpets, and and slightly better low down, thats on a 410 BHP engine.
Rescued attachment engine1.JPG

Ive got an ITG megaflow on mine, but I have got 2 ITG foam filters for sale (1 for each carb).