CNR - Because these are forward clicky switches, the partial depress for momentary ON has never been a problem for me. I have found the additional pressure needed on my P10C to fully click it ON can cause it to slip in my hand if I am not gripping it tightly enough. Now, I also have to qualify things a bit...my hands/fingers are probably slightly larger than average. The "cigar grip" holding style and thumb activation of the buttom didn't work for me with the P10C due to slipage of the light body between my index and middle finger or my thumb was just too big to get past and down into the tailstanding portion of the tail at certain thumb angles. As such, I would normally hold the light with the tips of my thumb and middle finger and activate the clicky with my index finger. Yes, a few times I have found that I either could not or did not apply enough pressure on the clicky to fully active the switch and had to regrip and tighten my grip on the small body section to retry to click it fully on. Anyway, late last night I found an O-ring that allows me to activate the P10C clicky consistently now with either aforementioned grip. This O-ring partially "rolls" along the body/tail flashlight surface when my fingers are pulling on it during button activation (which will still take some getting used to) but my grip does not fully slip anymore. The O-ring only rolls back where my fingers contact it and this distance is about equal to the thickness of this O-ring (approx. 2 mm). Full rolling of the O-ring is limited because it fits snuggly against the underside of the clip in its "proper" position (at the joint of the tail and body sections). Since the space between the clip and tail narrows right at this body-tail joint, the already snug fit of the part of the O-ring that is under the clip prevents its movement and limits the maximum movement of the rest of the O-ring to whatever its particular elastic properties happen to be, (i.e., you want a less elastic O-ring for this application) I happened to find this particular O-ring in an assortment that I had obtained some time ago from the plumbing section of Home Depot!). Regarding the T10C (even given the limited time of ownership), clicky stiffness, slippage/missed full activation are non-issues, due to its specific body and tail/tailcap design. No problem for me with either grip.
Regarding beam differences, even though both lights are fully regulated and I don't think it should make a significant difference either way, I am currently recharging batteries right now so I can make sure I am comparing fairly (matching brand, capacity and age of batteries). I will reconfirm my initial white wall beam impressions and also compare both beams outside, after dark (the best time of the day!). I will try to post again later this evening and will happily share my personal, albeit subjective observations.
HSG - BTW, do you know if the stock P20A2 head/emitter/light engine will run with 3.7V RCR123's or just 3.0V Primaries? Also, I like the extra knurling on the P20A2 head for changing from low to high (general to turbo).