Got a coin, flip it. From a performance issue, maybe a nickels worth of difference. I would give Win 7 the edge in stability, that is recovering from a wayword app.
XP may be dead, BUT it's a long time to burial.
Is it worth the cost to upgrade - ??? depends on if you need a feature. IE I have a 128 Gig SSD for laptop (#3), win 7 has trim, XP does Not. As far as applications go, Mine all run on either, I have none that requires Vista/Win 7.
If Money is tight, don't, if money is not a object and / or you need a funtion that is in Win 7 and Not XP - by all means get it.
Do not let the "Future vs dead" enter into it - When it becomes YOUR future - GET IT.
PS have 3 Laptops, 1 XP, one all three (Have a 3 HDD one with ea) and One Win 7 on SSD, Vista on HDD).