On level 47 you have access to Bigfoot Country . There are no enemy armies in this area - besides the missions. But you can raid on this territory. For every battle you earn 476 sp and about 2500 gold. With light Chem Tank or many other units doing damage in more than one field this can be done in 3 turns and every battle takes only 30 seconds. Without boost you can make up to 72.000 sp and 350.000 gold per hour.
There are some combinations when one can get as many sp per hour by using heavy farms with walls or fences and promoting demolishers (assuming a in-game friend supports you with constant drops; no double use of course), but usually farms will give max 40.000 sp per hour.