The issue of Safari reloading pages when switching tabs drives me nuts as well. Funny thing is there seems to be no consistency, sometimes when you switch tabs it won't reload the page and sometimes it will, even if you have only been away from a tab for seconds many times it will reload the page. This defeats the purpose of opening a link in a new tab to save the time of going forward and back again.
Also Apple please give us the option to open a link in a new tab without immediately switching to the new tab. I want to open links in new tabs for later reading, not immediately.
Depends on how many tabs you have open, how much data was in those pages, what other apps you've been running - sometimes I switch to another app, get something, then come back to find that tab issue. There's lots of things other than just the tabs and number of tabs.