Been using Arctic Silver 5 myself for the better part of the past decade, I see no reason to change from that position. Since CPUs are designed to (literally) run at up to 1C below Tj-max before the thermal circuit executes a shutdown for protection if it does reach Tj-max (and run at those kinds of temps for years continuously) I don't really give a damn about temps anymore. I regularly push my i7-2640m in my laptop (which runs hotter than a desktop by default anyway) doing x264 video encoding and it'll reach 98-99C for hours at a time and I couldn't care less - yes I redo the thermal compound about twice a year and clean out the ventilation on the heatpipe vents but it still runs hot regardless.
I think people focus a bit too much on temps these days, if you're going to push the hardware to its actual limits you're going to get heat from it and there's really only so much one can do. I've seen some rigs where the cooling system put in place was probably over half the cost of the system's total price and it still runs hot by my standards.
The silicon will probably be fine with it.
But there are an awful lot of mechanical connections in your computer as well that you don't often think of. The pins mating inside the socket, the solder joints on the motherboard, the traces on the PCBs. Those all flex as they heat up and cool down, and the bigger the difference between cool and hot, the more the flexing. It isn't much, but it all adds up over time. It attributes to weirdness - finding a power cable loose on a hard drive after it hadn't been moved and had been working fine for 2 years. Video card needs to be reseated in the PCI slot for no explicable reason, cap decides to snap one lead off the solder joint, etc.
You can't eliminate thermal expansion entirely. But you can mitigate it. Odds are something in your computer will break as a direct result of mechanical disturbances due to thermal expansion before any silicon actually fails because of dielectric degradation.
Also, I have some AS5 and AS Ceramique in a drawer, both are years old and still get used on my builds. Love them both, both work well and hold up well long term, but ASC is a bit easier to work with (less sticky)