Pt => blink on slark is the biggest garbo I've seen, midas as well
You have a 800 hp 80 dmg hero who gets blink around level 8 and what then? Go around when you can't even solo kill a support alone? You should pick a different hero if you intend to go safelane and rush boots into blink because slark isn't supposed to be played like that. Centaur, tide, panda, legion, slardar, ursa etc should be your choice instead.
What do heroes that buy blink have in common? In 90% of the cases they buy it because they:
1) Have a melee range aoe stun/slow that they want to initiate with and have no way to hit it otherwise 2) Have a impale/aoe disable that they want to hit the most possible heroes with
Slark has a pounce. Pounce is a 1 hero (not impale lined stun that you need to position yourself for) bind that has 700 range. Level 7 slark with blink isn't even close as good as is a level 7 centaur/panda/tide/slardar/sand king with blink. What does he even do? Pounce for 240 and hit for nothing? Maybe if you play him as an offlaner and go around with your supports and create space, otherwise it's terrible.
The thing is, people play this hero similar to storm where they go and walk around on level 6 and lose themselves the game. It will work in ~50% of the games. Slark is one of the hardest lategame carries with items, and yes he will wreck almost any other carry due to his skillset. If you have items, you 1v5 fights. Hero peaks on level 11, when he has both nukes maxed and enough regen from ult to sustain himself in the fight and speedfarm the jungle. So sit on your safelane with a tp ready only for sure kill counterganks.
Why pt aquila drum? Well this hero is hard to gank, but a 800 hp slark can die in a stun. A slark that has 1200 hp at 10 minutes doesn't die to anything other than 5 heroes, as simple as that. You can't force him out of the lane, if teamfight breaks out at your tower it's likely that he will be able to take 2+ heroes on by himself due to sheer bulk that most people aren't used to facing. He will take the safelane tower due to one hero unable to defend it since he'll just get dived and killed. Drum speed boost always gives extra kills and easy pounces on fleeing targets.
Now we go to the blink vs shadowblade debate. Shadowblade is a superior item in 99% of the games, no matter in which bracket you're playing. The other 1% is when you buy a 5th-6th item blink when you have abyssal and you're playing against a divine ember, gem storm , 5 slot void and similar stuff.
This hero thrives on solo killing. The more heroes slark in your game can solo kill, the bigger the map presence he exerts is. 30% aspd and 30 damage for 3000 is amazing, the item almost pays itself out just from stats alone. Then you get the 175 backstab for a total of 205 burst damage added on the first hit. Ludicrous.
Slark instantly detects when he's seen, meaning that with SB you instantly know where sentries are placed and can react accordingly. Imagine that the enemy team is pushing under sentried area and you want to take a fight. Well, blink would be an obviously better choice, right? Wrong. Pounce has 700 range, I can just walk in and pounce somebody right out of SB. And what now? Well now I have 30 more aspd and damage than I would have with blink. Half of the heroes can't even do anything, I will just hit them out of SB and then pounce, even if they have sentries down. And I will bait disables by instantly pacting out of SB once I know they see me, that's how lions and rhastas die.
Shadowblade provides an infinite fight resetting tool, blink doesn't because you spam pacts in a fight and cancel it yourself. Pounce over cliff into invis into wrap around gives you 100% hp and an opener again easily. Fights usually become chases and the other team strays away from the sentried area while their supports are dead. Easy kills. You've got to truly master the hero to appreciate the amount of maneuvering ability SB gives you, even against a gem and infinite sentries it's no problem. Cores usually won't be carrying reveal as well.
Oh and yes, sny > skadi in 99% of the games. Bulk + more damage for cheaper cost so you can keep overwhelming your enemies. The ultimate orb progression is way too slow and bad and is only good when you can farm a skadi very fast and you're playing against a hero that's severely crippled by the 45% aspd debuff (think sven, TA, void, wk etc)
link to post-http://www.playdota.com/forums/showthread.php?t=1442049