UPDATE October 7, 2015: The evening event was even more crowded than the unveiling, so hands-on time was still at a premium.

I brought along my Surface Pro 3 pen and I was able to confirm that the two pens are interchangeable.

The inking experience is exactly the same between the Surface Pro 4 and Surface Book. The detached Surface Book display is amazingly lightweight.

Tactile feedback with the new pen's nib and eraser was significantly better. I was only able to test in OneNote, but varying pressure provided different levels of drag that are not present in the old pen.

Drawing out slow diagonal strokes with the SP3 pen, it was impossible to avoid jitter. With the new pen, jitter was still present, but dramatically reduced. Increasing my stroke speed slightly eliminated the jitter altogether.

The eraser tip is amazing. Truly feels like a rubber eraser.

The pen has a magnet along its flat edge that connects to other magnets in the Surface Pro 4 and Book. The SP3 pen will attach to the new tablets but the magnetic hold is much weaker.

The keyboard of the Surface Book is much better than the type keycovers of the Surface Pro 4; however, the keyboard is still inferior to the typing experience offered by a Lenovo Thinkpad.

The larger glass trackpads are excellent: probably the closest to Apple trackpads found on Windows devices.

Battery life of the Surface Pro 4 is 9 hours. The Surface Book will offer 12 when configured as a laptop. But when the Book's display is detached, it will only achieve 3 hours.

Microsoft representatives were tight lipped about the precise hardware choices in the two devices. All I could get was that both use sixth generation Intel Core CPUs (dual core, not quad) and that the NVidia gpu in the Surface Book is a custom design.

The choice between the two really comes down to how much importance is placed on lapability, keyboarding and GPU performance. Gamers, animators and video editors should clearly choose the Surface Book. Artists should be more than satisfied with the Surface Pro 4.

For me, I'm looking forward to trying out the entry level Core M Surface Pro 4, which is $899 and will be the only fanless device in the lineup. The reduced weight and thickness, silent operation, long battery life, larger higher resolution display and improved pen should make it the ideal mobile sketchbook.