If you're buying the machine in its netbook role, i.e. you want to be connected and do most things such as email through a web browser, then I think this Vaio is free when you sign up for a Vodafone dongle at 25 quid/month over 2 years ("T5" suggests you're in the UK).
Win 7 Starter limits are 3 applications active at one time (but you can have multiple windows open, so maybe not a real limitation).
If it doesn't feel fast enough for you, then I don't think upgrading the Windows version will do much for you. Adding a bit of memory might. It depends what you mean by "poor".