Interesting. I wonder if the bottleneck is one of the Wine (Windows 'emulation') libraries. Assuming that you compile the Windows version under Linux against the Wine libraries bible_pay?
I have also noticed that the wallet uses no pagefile resources at all, so a bottleneck could be possible.
Unless you don't have much memory in your computer I wouldn't expect the wallet to need to use virtual memory (the pagefile on the disk), which is a good things as using memory in the pagefile really slows things down. The resource intensive aspect of the wallet is processor usage for mining.