I mean, sometimes bitcoin network is overloaded and transactions goes too slow. Where I can see this info in numbers ?
I suppose you're talking about the unconfirmed transactions in the mempool...
This site should give you an idear :
https://blockchain.info/unconfirmed-transactionsMaybe this is what I want, but how can I estimate bitcoin load using info given on that page ?
Some clarification of what I want: 500 bytes transaction with 0.0001 btc fee was processed in 10 minutes when system was 10% loaded
and 500 bytes transaction with 0.0001 btc fee was processed in 2 hours when system was 90% loaded.
I want to go to some page and see "Bitcoin network is loaded on 90%", then I set fee 0.0002 for 500 byte transaction..