An email from Debian Project News recently informed me that the 686 flavour kernel is to be dropped.
From the information linked to at Ben's technical blog, it seems I'll be able to use the '686-bigmem' flavour- even though my computer only has 1GB of memory- with a tiny hit on performance but a slight security advantage:
Even those that have less than 4 GiB RAM do support PAE and can run the '686-bigmem' flavour. There is a small cost (up to about 0.1% of RAM) in the use of larger hardware page tables. There is also an important benefit on recent processors: the larger page table entries include an NX bit (also known as XD) which provides protection against some buffer overflow attacks, both in the kernel and in user-space..There are a few 686-class processors that won't be able to use 686-bigmem and which will have to use the 486 flavour- apparently with a performance gain (see the blog for details).