Personally, if your looking to spend almost ?100 and your looking for performance, first of all how far are u prepared to go in the grand scale of things ....
If u wanna see big gains quickly, save the money on the air filter and think ahead to chips, cams and head work. If it's pure power your after ultimately that's were you'll end up after spending ?500 on a full stainless exhaust, induction kit, manifold HT leads etc and only see say 5 bhp increase. Not alot for your money!
Everybody is quite right in saying it's the overall solution that provides the performance - but unless money is a major factor don't always think small first.
?500 on a cam(s), New ECU chip and mild head work would see anything up to 20bhp increase - then surround these with exhausts etc.
Really it's personal preferance, but coming for a BSc in Auto Engineering i'd take? much bigger steps initially as there's alot more to gain at the start.