Just as an update, I got my D10-GDP over the weekend, and had some time to play around with it.
I really do like the beam -- its smoothness is great, and I can't take good enough images to do it justice. When next to my OLight T15 (Q5) the smoothness does make a big difference. I think it's fair to say the pattern resembles that of those SSC P4 lights like the LumaPower LM31/LM33's.
Does it make a difference? IMO yes, particularly at lower brightness levels, when you're trying to illuminate things close by (i.e. looking for something you lost), it's much more usable than the Cree pattern. However, the hotspot doesn't hold as tightly as the Cree and if you're trying to throw long distances, the Cree will beat it hands-down. However, IMO as an EDC close-range illumination is the name of the game. When driven at max compared to a Cree driven at max, IMO the GDP's color rendition is a bit warmer and more "realistic" though it's hard to discern that difference on photo. Also, there is NO blueness or purpleness at any level in my testing.
Something odd that maybe a light guru can shed some... light... on, when whitewall hunting the Cree looks "warmer" tinted than the GDP, which looks really cool white. However, when shining like a wood surface or something else colorful, the GDP seems to display its colors much more realistically while the Q5's portrayal looks somewhat pale.
As far as inductor whine, it is present on highest on NIMH, disappears about two steps down from highest. No big deal to me -- I am pretty sensitive to high pitched noises but this doesn't bother me at all unless I hold the light right up to my ears on max brightness. I find myself mostly using around 75% brightness anyway so it's less of a deal.
The UI is great -- by far the best light UI I've used so far. Easy to switch, rapid switching on and off doesn't activate some secret hidden SOS mode, fully one-handed operation. The grip is also very great -- the knurling is perfect. IMO the D10 is just the right size -- I would imagine the EX10 too small to confidently grasp.
Oh yeah, so far I haven't found any quirkiness with the piston-drive on the factory lube.