Whats the most reliable link for network hashrate?
Edit:
Also I am getting a little confused with the difficulty retargets being extremely slow, and what this means for if everyone jumps off as soon as the difficulty increases?
Is it better to mine with a high or low hashrate to difficulty ratio? Haven't thought this one through, although I'll try
For almost exact numbers you need to visit the pools and add the rates together.
bitmark.co/statistic/health updates every 60 blocks
in the client you can do 'getnetworkhashps xx' where xx is a number of blocks, advise over 20 due to the randomness of finding blocks.
there are data sources too under bitmark.co/statistics/data/ if you need them.
The difficulty retarget is every 720 blocks, and currently everybody is jumping off, they'll jump back on when it changes I'm sure. So it looks like for a while the difficulty is going to quarter and later quadruple until the cycle is broken by increased demand. The down side of this for miners is that they're making it more expensive for themselves and locking up their newly mined btm for ages. The upside for everybody else is that btm being minted is effectively slowed 2,3,4,5x and new currency minted is locked so can't make it to market. This helps stabilize market prices.
As for your last question, if we simplify it you can mine twice the blocks at half the speed or half the blocks at twice the speed. which is more 2*0.5 or 0.5*2? The percentage of BTM you gain on average correlates directly to your percentage of network hashrate. Difficulty determines the speed at which blocks are found by the network on the whole, it is a target hashrate for the network to reach based on the last 720 blocks average.
The answer to all of the questions succinctly, is that the optimal current network speed for miners is 6 GH/s to maintain a health stable network and fair profit, anybody who mines consistently regardless of network speed or difficulty will always have the lowest overall cost, anybody who jumps on and off will have the highest.
There appears to be a huge amount of misinformation given to miners, even things like profitability calculators, to calculate a profit on currency which cannot even be moved for days with fluctuating markets is pure speculation at best, outright lies at worst.