A couple more thoughts:
Approach speeds in this case should be predicated on aircraft performance (factor in A/C weights, too), pilot experience, terrain, entry and exit paths- lots of things that would make me loath to say 40, 50, 60, or any fixed rate of knots. Some aircraft are harder to slow down in a descent. Some require speed to keep emergency maneuver capability. Altitude or airspeed, keep as much of both until you can't anymore, and usually you can carry speed longer. Suggestion- try to keep best glide speed (at least) through the transition, down to 2-300 feet absolute altitude (approach initiation point), when you're on angle, to your high hover point for the vertical. 70 kts or so in a 350, 60 in 206, etc. You'll know you had too much speed if your approach descent requires big power reductions to keep on angle, or slips. Do it again, slower.
Don't restrict yourself to conventional airplane patterns. Circling transitions, at least down to the initiation point (2-300 feet AGL) are a good way of keeping the LZ in sight, being neighborly, keeping forced landing sites in range and controlling speed. If you have good LZ location, you can also zig-zag, dog leg, what ever, the transition. Do it over the best escape terrain, within performance limits and flying neighborly.
If you gotta do it crosswind, put the wind on the strong side, i.e. right side for French products, left for the rest of the world (unless you're in a Bell...). Easier to reject the approach.
As the man said, above ETL, you don't have much to sweat regards vortex ring. If your approach involves extreme descents/speeds, however- abort. Your plan is flawed somewhere.
If you have to zero airspeed and continue a descent, slow is the word and high is good to make the transition- until you have more experience as to the dangers and trades to minimise hazards.
Descending into a hole, limited escape options, is not the time to get impatient or careless. 200 fpm vertical descent, is safe, slow enough that location in the hole is manageable. From a 100 feet, it's only 30 seconds at that rate. Don't rush it.
This is all a process trading helo flexibility against risk. Survival first!