PostgreSQL block size vs. LVM2 stripe width

I have some results from DBT-2 testing PostgreSQL with difference block
sizes against different lvm stripe widths on Linux. I've found that
iostat appears to report more erratic numbers as the block size of the
database increases but I'm not able to see any reason for it.

I have pg_xlog on a separate set of drives from the rest of the database
and was wondering if having different block sizes for the log and the
data has been discusses?

Or does anyone have any tips for an optimal combination of settings?

Here's a summary from an Itanium2 system, where bigger is better:

Linux-2.6.3, LVM2 Stripe Width
(going across)
PostgreSQL
BLCKSZ
(going down) 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB
2 KB 2617 2656 2652 2664 2667 2642
4 KB 4393 4486 4577 4557 4511 4448
8 KB 4337 4423 4471 4576 4111 3642
16 KB 4412 4495 4532 4536 2985 2312
32 KB 3705 3784 3886 3925 2936 2362

Links to more data:
http://developer.osdl.org/markw/lvm2/blocks.html

Mark