Many thanks for the replies.
Yes I'm looking to use the laptop with an RME interface of some sort... I'm hoping I might be able to use my existing Multiface 2 with express card, in fact...
It's possible I might be using the computer live on tour, hence I need to achieve rock solid performance and reliability. Even a tiny extra edge offered by better disk performance is of interest.
Thanks for the comments re. the system drive, Exalted. Could there be a potential advantage in terms of long term reliability, at least, in using an SSD for system drive?
For the best performance use a PCI Expresscard which should work fine with the Multiface.
Get a large fast SSD which you can put the operating system and all your samples on. They are so quick that multiple drives are not necessary at all. Its really shocking how slow a PC feels on a hard drive when you have got used to a SSD. I'd really recommend them to anyone.
As for reliability - just get an external backup drive and keep it updated. Some SSD manufacturers are better than others too. OCZ are crap, samsung and intel are very good.