Hey,
We do heaps of these for customers. It is really not about the specific performance, everything is with a few %. If you have got a specific use case, do the hard yards and run the tests yourself. If your order is a few hundred units, the vendors or your SI will help you out with demo / eval units. We had customer wanting W7 tablets, we supplied demo units from 3 vendors and we ran a large number of tests. The most important to them were form factor / weight / durability / battery as you would expect. But the performance of the WWAN 3G card was a key indicator as well. So check what you actually need, if its just "good office performance", then anything is fine.
Go for the soft benefits - support online and directly to the users desk, the warranty period and the price. Also longevity of chipset, lifecycle, accessory cost etc.
We have the first customers rolling out entire fleets of SSD now, they are awesome in laptops and tick the green box in desktops too.
Cheers,
Mike