I'm pretty surprised to hear "MegaBank" ran AMD. Not that Opteron wasn't awesome and better than what Intel had at most things, at least until Woodcrest if not Nehalem. But because MegaBanks are usually pretty conservative. More than a few still run mainframes and proprietary unixes.
We wrote quant code that had to run on all architectures... for the HFT team [1], unfortunately, including a long drawn out debacle supporting Solaris 5.7 for an absurdly long time. Other members of my team were looking at IBM architectures as well, mostly because IBM were throwing money at us to use their kit.
[1] high frequency, not necessarily low latency, for some defintion of the word 'high'.
Unless you worked in their HFT group, that is.