Thanks all, some good discussion so far.
I think turning downwind before reaching circuit height is probably the best place to start to keep the downwind closer in.
I had never considered the 15deg limit could be related to climb performance rather than stall margin. The PA38 stalls at 52kts clean, the stall speed at 30deg should be 56kts so 70kts should still give a good margin. However, I'll stick with 15deg base/final turn.
I see both sides of the "within gliding range" argument, my method so far is to keep a little bit of power on and use the flaps from the start of the base leg with full flap on final. Still much steeper than the PAPIs though - not dragging it in with loads of power.
TotalBeginner - I've not flown a PA28, but when getting back in the Tomahawk from a 172 the flap difference is noticeable. Hopefully someone will have some advice for you regarding the Archer - good luck!
-j34-