Originally Posted by Rossco

Kelford 262's if you want a smooth idle with a good midrange punch and better high rpm breathing.

Chances are your v5 heads will be cracked around the spark plug threads (most do) - go with GD wrx heads (bigger ports than V5/6) and use your current shim under buckets to convert the GD wrx heads to shim under.

I run Brian crower 272's and still get around 500km per tank average - it's all down to how much you are prepared to spend on tuning & dyno time.