Well the Soul Spear is not trash, but it fades in comparison with that Impaler. It is slower, requires higher level but is not much stronger. But really, the Impaler is a gem EDIT: Out of curiosity, I went to my DPS sheet to do some calculations, and I found that I would actually get higher DPS when bossing (using Stoppers) with that Impaler. My current spear is speed 6 (compared to Impaler's 5) and 119 ATT - and I paid 2.1B for it. This won't mean that the Impaler is necessary worth over 2B though. Higher ATT has an advantage when grinding, and in all situations when you're not using high-attack pots. EDIT 2: I posted some misinformation here earlier, but it's fair to say that the Impaler will outdamage higher ATT weapons to some extent, depending on how much extra ATT you have from other gear + potions.
Greetings, while this is slightly off topic, I would like to correct you on your dps comparison. Your Sky Ski has an attack speed of 4 after booster, which correlates to 930ms (Spear Crusher). The Maple Impaler, after booster, has an attack speed of 3 (870ms). Using the formula provided by Ayumi database, you would need an additional 316 weapon attack for the Maple Impaler to out damage the Sky Ski, which is unrealistic. Assuming no additional weapon attack, using stoppers with the Impaler in question can out damage a Sky Ski with 101 attack. Any higher of a differential requires other sources of WA from equipments. Hope this was helpful. Provided is the link to the aforementioned database: https://ayumilovemaple.wordpress.com/2009/09/06/maplestory-formula-compilation/