HD I agree that is best for long/departure-only runways.
I work at a mixed mode (short!) runway. Whenever possible I "chuck" as early as possible (at my unit procedure is to check SSR code first - no SMR), however, we also need to protect against piggy-back go-around scenario so it's not possible during peak hours (obviously if the weather is poor - low cloud/low vis - we increase arrival spacing to ensure we have separation if this occurs). In good conditions, where we can visually separate if there is a missed approach, we have tighter arrival spacing. In this case we hold on to departures for longer (until the SID track takes them away from the missed approach track) - generally until the first turn. Once that occurs, or we have seen a successful landing, we "chuck" to radar.
The first turn on our SIDs is either 1 or 1.5 DME and most departures are around 1000ft or above at this stage (due to steep climb gradient).
Likewise we have tried polling pilots to get a best-time-to-transfer and trialling different procedures but with inconclusive results.