I followed Top Barks recall lessons and can vouch for their efficency. 
Today, my girls were in hot pursuit of squirrels
but a toot of my whistle bought them both running back instantly. 
My Acme is a 211.5 (cos that was the only one that came in purple, at the time
)
I have the whistle recommended by Top Barks and have also been following his reliable recall thread. Still on the long line stage though after a long time (couple of months). He is OK if he hasn't got a scent/seen something to chase/play with. He knows the whistle means come back and you will get a treat but he is by no means consistent. I still only blow it when he is on the way back to me already as if he isn't, he often just carries on sniffing or whatever so I have to reel him in in order to try and maintain the conditioning. I didn't start with the whistle until he was 9 months old (wish I had started on day 1!) and I think he will be on a long line forever! (BTW the only place I let him off lead entirely is I use my own whistle/call but not the dog whistle - feel mean having him on the long line all the while although he doesn't seem to mind).
Good luck to the OP. Would be interested to know how long it took others using TB's method to get off the long line? 
It took me 5 months with Alfie, but then I wanted to be sure as i was walking him around sheep at the time, I didn't fancy explaining to Penny B that the dog i'd just adopted via her had been shot for sheep worrying.
There is no set time, i could have done it earlier I'm sure, I guess I'm just cautious.
Caution paid off as he has the keenest recall of all my dogs.
I also think it depends on the relationship you have with the dog, I'm the second most valuable thing in his life and i'm usually holding the most important (his ball).
Do you guys ever just sit and feed and cuddle on walks? do you just sit and chill out together, i do lots of this alongside the training.