Basil, I assume you are aware that 802.11n is as yet unratified, and anyone selling such kit is taking large liberties!
If performance, weight and battery life are an issue, start looking at solid-state drives - 32GB flash SSD drives (PATA) are now available, costing about £350, but are way faster than conventional HDDs, weigh less (for a comparable capacity) and use less power. Expect about a 15-20% performance boost, plus about 10% longer battery life.
AFAIK, 64GB SSD drives with SATA interface are slated for early next year, or even sooner.
SD