Slayer is a fun method to improve your melee skills, therefore, if you are planning on engaging in training, do it. It's a great way to break the monotony working on cheap runescape gold one monster. You're clearly not a person who has 85 Slayer, Abby whips are approximately 1 in 540, not the 125 kills you can get camping. The biggest gain in Slayer comes from not the major drops, it's those little ones that add up over time . Along with clues in case you make these and skilled at running herb runs between your tasks.
It's true, I dont have 85 slayer. However, it doesn't mean I don't know anything about it. There's been stories of people not getting a whip drop in less than 4-6 hours of relentless killing. The truth is that whips are one of the rare drops. Any help site you visit will identify the whip as one of them.
The chances of getting whips within a 75-125 kill range is possible, not tipacal, but feasible. You stand a better possibility of getting it within the 1-540 range. However, you might not receive one. Also, if you inquire about the reasons why people train slayers it's nearly always about the large drops. Examples include whips from abby deamons, sol from ice strykewyrms, and so on.
Although they may be able to slay for those drops most of their profits will not come from them especially when it comes to ice wyrms. that have spectacular drops, the SOL is just a tiny extra. The 1/540 comes from the typical drop (mite be 520 but I'm not sure) but it is due to players submitting the number of kills are required to earn a whip, yes its possible to get the range you want, but that's not the drop rate.
Helm of Neitiznot - It's a good 'balanced' helm, get Verac's/Torag's helm to get more defensive stats or a Fighter hat to increase offensive stats (about exactly the same statistics as the Rune full helm but with with bonuses in Crush, Stab and Stab, Slash and Crush attacks)
Guthans Plate: Decent, Fighter torso gives a nice Strength bonus so it's an excellent choice for those who can't afford Bandos but I'm also not entirely certain about this, but I'm sure that the Torag (and Dharok's) is slightly superior defensive statistics and is worth 650kish so it's worth considering.
Your current setup is great but I'd suggest an option that doesn't diminish. Dragon Platelegs with Fighter Torso, for example. Dragon Platelegs cost runescape old school account a reasonable amount and the Fighter Torso only costs a couple hours to obtain. Or Bandos armour if you're a very wealthy player.