Ultrasonic sensor SRF02 and SRF05 - quick question

Hi guys, i want to measure a container with bottles inside with 2 sensors i want to use the SRF02 because it has a bit smaller beam width i think(correct me in i'm wrong) but i heard many people say that they have many problems with that, and that the readings sometimes are off by many inch/cm.

I want to use the SRF02 but if it justifies i will use the SRF05 the only problem is that it is more expensive.

I want to wake up arduino and send by gprs the distance, will i need to measure like 20 times and then calculate the average value? Or does it returns stable values? (I dont have one wich i can test).

What about the power consuption, it says 4mA but only when ranging? or always 4mA when it is just connect? Because i will only measure the distance twice a day, if that happens i will add a transistor to cut the power off it.

Another question, i read somthing about tunning in the datasheet, and it takes maybe 5 first rangings for it to "tune up" ? Or does it measure good the first time it is powered up? it says the first time the minimum range is like 28cm and then gets smaller everytime with the tunning ? till the 16cm?

And what about the sensor adress, will it reset everytime i cut the power supply or will it stay always with the adress i set it to be?

Sorry i have many questions, but i really need some info i couldn't find in the datasheet or other websites and forums, so if anyone knows anything please share your knowledge please.

Thank you guys!

Anyone on this?!? I am also interested in this matter!
Please someone with experience on this could give their opinion?

Maestrini Manuel