I've been building PC's for a local computer shop, (everything from high end, water cooled gaming rigs, budget builds, cheap email boxes, linux rigs, servers, parts bin rigs, and everything in between,) myself, (usually nicely spec'd budget gaming rigs and home media servers,) and family, (modest "future proofed" and parts bin builds,) for about a decade.
I've used a lot of different thermal pastes, including the pads that come on stock coolers, pastes that come with aftermarket coolers, glues, ceramics, copper, silver, some weird white stuff, lots!
The Arctic Silver 5 has, in my experience, consistently lowered temps and helped to get the most out of any cooler I've purchased for myself, someone else, or a clean out of an older machine.
I'm really impressed by the features AS5 has up it's sleeve.
Pros:
-It's performant. Even on chips that I've uncovered from "custom builds" from others where the CPU heat spreader is scratched, or a stock cooler has a poor finish, AS5 seems to improve performance ALWAYS. Even if it's one degree, or keeps the temp down an extra minute or so on a failing part, it works very, very well.
-It cleans up very easily, even after being caked on for years. (A bit of isopropyl alcohol goes a long way!)
-It keeps a long time. I've found tubes of AS5 in tool sleeves that I've lost for a year or two, and had no issue using the AS5 in the tube. Most other included thermal paste/greases I've used will harden or get gummy.
Cons:
-It seems to not be available locally. If you need to run out to a local supply shop I've usually only found other products, so I make sure to have some on hand.
-It's the same price per tube as much bigger tubes of others. I still think that due to how well it performs, it's worth buying more often.
Bottom line:
-If you're installing a new CPU, cooler, building a new PC, have overheating issues, are cleaning out an older machine, give AS5 a shot. It's a very good performing product, and for a few bucks, it's often the saving grace that can restore PC/hardware performance.