32 bits are better than 64
 

Sometimes

RECENT TESTS conducted using a Small Business Transaction Benchmark from Neal Nelson showed that a 32-bit version of Suse Linux Enterprise Server 10 provided up to 37 percent more throughput than a 64-bit version.

The tests were run on a computer with a Tyan S2881 motherboard and two AMD Opteron processors.

A bloke from Novell said he wasn't surprised.

More here.