In my experience managing workstations over the years, reliability is honestly the most important thing when you're on a deadline. I've tried many used cards to save money, but the lack of a warranty always makes me nervous when a project is due. For your 4K wedding edits, I really think you should stick with something new and stable. I highly recommend the ASUS TUF Gaming GeForce RTX 4070 Ti Super 16GB GDDR6X for a few specific reasons:

• Dual NVENC Encoders: The 40-series has the newer dual encoders which are a massive help for fast exports. It handles 10-bit files much smoother than the older Pascal or Ampere chips in my experience.
• VRAM Headroom: 16GB is the sweet spot for multicam. Premiere needs that memory to cache all those different angles simultaneously, and anything less will start to stutter.
• Power Efficiency: A used 3090 is a power hog and gets incredibly hot. The 4070 Ti Super is way more efficient, which means less heat in your studio and less strain on your power supply. Honestly, buying a used 3090 right before a big deadline is just too risky. The performance gap isnt big enough to justify the gamble on a card that might have been beat up by the previous owner. Stick with the 4070 Ti Super for the peace of mind and the better encoding tech.

^ This. Also, dont overlook the ASUS Dual GeForce RTX 4070 Super 12GB if you want to stay well under budget. It handles those 10-bit files easily. Tho if you find a clean EVGA GeForce RTX 3090 FTW3 Ultra 24GB, that extra VRAM is a lifesaver for multicam. I switched to a 3090 last year and honestly havent had a single crash. Its been rock solid for me.