Okiez, first up: My experience with the game is becoming slightly dated since I haven't played in several weeks. I mean, it's not like I'm totally clueless, but all I have to go on for new changes are patch notes, Council forum access, and intuition. It's pretty good, but not as good as actually playing the game.
Nasus is silly good. When playing against a Nasus, you HAVE to disrupt him. If you let him farm his SS to ridiculous levels it's GG. That being said, this is not very important right now as high Elo games are fast and furious in the current metagame. Most are over / decided by 15-20 minutes this patch. The pushing meta got totally revived as of late.
The real deal with Nasus is how gamebreaking his ult is in a teamfight. Tank him out (imo it's much better than going all those DPS items, since SS is item-independent. It obviously is better with items, but it gets almost as good when you're going tank, giving you the best synergy of invincibility plus ridiculous damage. Also with his the damage from his ult being item independent, it gives him crazy offense, and you itemize his defense, making the perfect hybrid) and own.
I haven't played the new Tryndamere, but *psst* there's some nerfs coming for him in the near future (next major patch). The next patch is gonna be awesometastic, almost as great as this one was for improving the meta. Long story short, yes, he destroys right now
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@Zeraph: Heal vs anti-heal is a very complicated meta problem to solve. Just last patch, healing was OP (at least in high tier games). You saw a Taric AND Soraka in most all competitive teams. People just didn't die; heal was far OP, even endgame. Now, this is where what I mentioned with my knowledge becoming dated comes into play: I'm not there to comment on the prevalence (or not) of S/T in high Elo play right now, cuz I'm not there ^^. But I don't hear people complaining that heal was overnerfed in Council, so I'm inclined to think that it's not yet a problem.
As for XP/IP: There never was nor will be a penalty for premaking. The 'penalty' for premaking is an artifical, temporary boost to your effective Elo. A 5 man premade has a HUGE boost to it's Elo, so if you're matched against solo queues, they will individually be much stronger players than you. As it is, 5 man premades statistically lose right now (they have like 40-45% chance to win from the matchmaker's point of view) because of all the QQ on the forums about solo v premade. MM 2.0 should fix a large part of these problems.
The penalty you were talking about comes from practice games. All practice games provide a -35% XP/IP gain. The teams must also be balanced (bots count the same as humans). This means you vs 5 bots earns you 0 XP/IP, but you vs 1 bot earns you 65%.
Also, once you reach level 11/12 (I forget which), you are only allowed 4 practice games per day. After 4, you receive 0% XP/IP.
86/64 seems pretty average for a nonboosted loss in normal games.