Just catching up here... if you need something that wont overheat during a Chicago wedding, the Nissin MG80 Pro Flash for Canon is a safe bet. Its designed for high-volume shooting.

• The quartz tube is very resistant to heat buildup.
• It works perfectly with the 5D Mark IV system.
• You can find them for about $400, which fits your budget perfectly.

Honestly, third-party gear is just not as good as expected when things get hot. Had issues with my Godox setup failing during a summer ceremony and it was basically a total disaster... wont ever go back tho.

• Just grab a used Canon Speedlite 600EX II-RT Flash if you want reliability.
• It handles heat way better for heavy shooting.
• Usually goes for under $400 used.

Jumping in here because I went through the exact same headache with my old V860 units. I got so tired of that thermal cutoff blinking at me mid-reception that I switched to the Westcott FJ80 II Universal Touchscreen 80Ws Speedlight and haven't looked back. Honestly, it handles back-to-back shots like a champ and I am very satisfied with the swap.

• Thermal management is the big win, it just doesnt quit like the cheaper stuff.
• Round head gives a much nicer falloff than rectangular ones.
• Color consistency is solid, saves tons of time in post. Since you're on a $450 budget, you could actually grab a new one and still have cash left for extra batteries. Found mine for a great price and it basically solved my reliability anxiety overnight... it just works every time. Good luck in Chicago!