The Dye will be quieter. You might notice a difference between the two in terms of accuracy because the bore sizes may be slightly different. The Dye UL backs are usually .688 and I'm not sure what the stock barrel is. If I had to guess I would say somewhere around .689-.690"
The Dye UL back I have is .692. I'm not sure what the factory barrel is either, but my paint rolls through it with no resistance, just like it does with my Dye back, so I think they're both nearly-equally overbored. I'm thinking maybe I'd be better off selling the back and using the money towards converting over to HPA.