Thanks for the replies!
Yes, I've realized that trying out more 60mm fan probably wouldn't be worth it. And yes, I was sucked into the "Stealth" marketing by Vantec. When I first used the 80mm Stealth I couldn't understand why there was a strange and annoying whirring noise coming out of my PC.
I first refused to believe that it was coming from the Vantecs but as soon as I took them out the noise went away. Even at 5v or 7v they still made that annoying noise. I don't even know why I bothered to think that the 60mm version might be different - stupid me!
I actually tried the 80mm-60mm fan adapter from Akasa and it works well after I covered up 3 of the side vents as there wasn't much air blowing in the middle of the HS (deadspot). But since I plan on putting a window on the side panel I kinda wanted to get back on using 60mm fans again to get a cleaner look. I didn't like the look of the 80mm fan sticking too far out.
Anyway, I ended up fabricating my own fan adapter from a scrap sheet of lexan and I now have the 80mm mounted to the Swiftech just like a 60mm fan. I also made little flaps in the adapter to direct more air to the middle of the Swifty and the temps are about equal to the Thermaltake 60mm (at 7v) but none of the motor/bearing noise....just a soft whoosh of air.
I want to try and improve the adapter I made but I haven't much free time lately. My PC is not silent but I can say it's pretty quiet.
Again, thanks to all and this is a great forum!