These are all questions I asked before I was afforded the opportunity to work with the HSMAdvisor software. I too own a 770 and it took me quite a while to figure out this software, let alone use it. Thanks to Eldar, the developer of the HSMAdvisor calculator I've manage to get it to work for me in the vast majority of cutting scenarios. The software has become very useful to me now but, nothing takes the place of hands on experience; which I don't have enough of.
I found that on my machine I could run it on the lower pulley for slightly more torque but, whether you use the upper or lower pulley both settings have their window of maximum torque. I've used the HSMA software to generate feeds and speeds using both the high or low setting on aluminum, various type of steel and stainless. I mainly use the faster/upper pulley just so I don't have to take the time to swap pulleys. For some reason I can't get myself to trust the WOCs that are automatically generated by this software when using my assigned DOCs. I've broken enough end mills doing this that in each case, even with the shallowest DOCs the pucker-factor is still quite high for me.
Something else I do that has nothing to do with feeds and speeds but more to do with speeding up the process of machining is, I'll set up all my tooling in their respective tool holders so they are all at exactly the same tool length offset. For me this really speeds things up. I do own the digial tool setter but this still seems just as fast for me. As far as generating overly aggressive feeds and speeds, I found this to be the case with this software; big time. In the HSMA software you can go in and edit the power rating of the 770 mill. It's rated at one horse power but, I edited this down to .75 horse power. I figured that If I could get the feeds and speeds recipes to come out on the conservative side I could then tweak those number upward until I got the kind of cuts and finish I was wanting. Before, when I tried the originally generated feeds and speed recipes, it cost me a lot more in broken end mills. It's much easier to tweak upward on an end mill that hasn't been ruined by being to aggressive.
There are also other features of this software that allows one to adjust feeds and speeds via some sliding scales and data input text fields that are quite helpful once you get the hang of them. It took me a while to learn just the little bit that I have learned using the HSMA software but, like I said, nothing beats hands on experience. It's that hands on experience that helped me make sense of the software and it was the workings of the software that helped me make sense of the hands on experience I've managed to get under my belt.
This is all old news to most of the seasoned machinist on this forum but, to guys like me who only uses my mill to run parts for selling on the internet about six times a year; plus oddball projects and stuff like that, it's taken me some time just to get this far.
MetalShaving