I find it hard to believe that tip tanks like these - on a Canadair CF-5 - hurt performance. I'm inclined to think they might enhance performance - once the underwing drop tanks are lost. Same with the F-105/CF-105 I'm guessing.
Materials, design, and aerodynamics moved on a long way between WW2 fighters and the CF-5.
My guess would be that for more modern jets with higher speeds involved, there isn't as much extra strengthening required for tip tanks, compared with the aerodynamic benefits (increased efficiency of the wing at low speeds, the tanks acting like an aerospike). But, that is just a guess, since I'm not an engineer.
Not only that, but directly in front of the intake is the wheel wells; you couldn't retract the undercarriage if you fit the tank. I'm surprised no one has mentioned the Cavalier Mustang, which, although not produced until after the war had tip tanks and were primarily intended as VIP exec aircraft, but were modified as close support aircraft for Third World nations. Performance doesn't seem to have been affected too much. It'd be interesting to find out about its handling.
ZK-TAF is a Cavalier Grant, if you get a chance to yarn with her pilots they'll be able to tell you. The RNZAF Museum's example is also a Cavalier sadly (ie, not original RNZAF bird, and very basic cockpit in comparison to NA machines)
Other post war birds with the tip tanks include the Jet Provost T.3 and T.5/ Strikemaster, and most modern trainers (Aermaachi MB326 and 339, for example)
Ddin't know that, Evan; might explain the gaudy orange and brown 1970s decor in the cockpit - ghastly! Haven't met Graham Bethell, but I hear he's a nice bloke.
I do like the Piper Enforcer; had a gander at the one at the USAF Museum once; very cool.