Ehhh... yes, 420, it likes twins, but that is still random, and the size of the planets of said twins is also random... so your comment is completely pointless. ^^;
So, Toliet... the best way to get a lot of 800+ is explore as many planets as you physically can. If you are a terran/a.miner/guardian, one "strategy" is to cluster together bad planets while you do not have any good planets... unfortunately, once you get one good planet, you cannot do this anymore as clustering it with bad planets will negate the effect. However, this DOES speed up 20% of your exploration time.