For Lightroom, I think the Thinkpad Tablet 2 might be a bit underpowered. Remember, the Atom SoC in it isn't just slow, it also lacks SATA controllers, and the eMMC interface it uses for its solid state drive is no faster than a SD card. And it only comes with 2G of non-upgradeable memory.
Have you looked at the (upcoming) Thinkpad Helix? It has a corei(5?) processor, proper SSD, 1080p IPS screen, active digitizer pen and a keyboard attachment with extra battery. It is, unfortunately, rather pricey (~$1400), although you could try to wait for sales and coupons. It has some cool abilities, like the reversible screen (for presentations/kiosk mode).
Surface Pro is another option. While it's still expensive, it's cheaper than the helix. Downsides are the low battery life (estimates range at 4 hrs) and I really don't like that there is no secure stow location for the pen. It attaches to the magsafe connector, but I'm worried that it would be easy to knock off and lose. Also, you have to remove it to charge the device, which means it could get left behind at home, at the office or at the coffee shop/airport kiosk.
Lastly, the sony vaio duo is another 11-inch 1080p convertible with a sliding keyboard and active digitizer. It's about the same price as the surface but with more RAM. Unfortunately, not only is there nowhere to stow the pen at all, the pen itself is not powered by the screen and instead uses batteries (AAA IIRC), so is thick and heavy.
Wind, Sand and Stars.