UA is a great company and the UAD-2 line is very popular with engineers around the world. However, in my case there's a BUT, it didn't help offloading as I was expecting it too.
My sessions on Ableton Live usually peak the CPU around 45 to 55% with about 30 tracks or so,containing around 6-7 third-party synths plugins. So, I thought buying the UAD Quad and replacing all the stock and third party dynamics plugins like EQs, Compressors, Limiters and Enhancers with UAD would ease the load... NOPE, it doesn't! I learnt the hard way after plunging a $1000 on the UAD-2 Quad card that dynamics plugins barely peak the CPU.
So, If you are buying for the pure fact and reason of mixing with UAD plugs then great, go for it. However, beware that the other advertising feature, offloading, may not do that much; especially if the taxing of your PC is coming from other third party synths and FX which the UAD card is not going to help offloading!
Very sad but I'm truly considering returning it :-(