Sleepy122 - Let's see if I can answer your questions. I'm terrible at composing my thoughts in short order so feel free to ask for more details if I don't cover what you need. Though I carry them a lot, I'm a pretty light weight user so these knives are never going to be stressed to the point of failure. They're not designed for punching holes in cinder block but you know that from having the T12CF. Having said that, they are both very well and sturdily designed. I use them for food, string, envelopes, occasional light cardboard, a bit of light crude whittling, plastic tie wraps, etc. and have never been disappointed.
Part of this may depend on how you feel about the steels used - ATS-34 with the T12CF and D2 with the E models. For the things I do, I don't know that the steel makes a large difference as long as I keep the edge up. I've not done much more than very light touch ups with an old, flat, smooth Gerber steel and then strop them on the leather steel cover. Properly heat treated D2 is supposed to be pretty tough and durable and I don't see much ATS-34 around anymore, but I think it is a decent steel.
The maximum blade thickness is about .087" on the T12 and about .094" on the E10. The hollow grind is very similar on both blades. Maybe a bit more pronounced on the E10 because it goes a bit higher on the blade and there is no top edge clip grind on it like on the T12. The maximum blade height on the E10 is about .985" and with the T12 about .910". The sharp edge forward of the choil is about 2.990 (3") on the E10 and 2.820" for the T12. The polished black coating on the E10 is beautiful and supposed to be much harder than the blade itself (I've forgotten the details) so should be durable.
On a crude food scale the E10 weighs about 2 ounces and the T12 about 1.5 to 1.75 ounces. Barely discernible to me when holding them.
Both knives have well formed thin handle scales - the T12 is carbon fiber as you know and the E10 uses machined aluminum. The slightly longer and taller aluminum handle may feel a bit better in my hand because there is a bit more to grab and the ridges on the E10 handle offer a bit more grip. The ridges are fairly smooth but I could imagine if one were to be doing some long, hard, tight grip, repetitive work with the E10, the ridges might bite a bit after time. I've never experienced this though. The smooth carbon fiber inlay fits well and feels good in the hand. It feels almost strategically placed to give one's more sensitive finger tips a possible break from the ridges - but like I said, this has never been a problem for me - just thinking out loud.
Both my E6 and E10 seem to glide open more easily than my T12. This may have to do with the T12 having the liner lock sprung against the blade or maybe just pocket lint. The T12 opens easily enough so I've never thought about adjusting it. I do try to keep any dirt and or lint to a minimum. The E10's polished coated blade may also have something to do with it. I have not taken either knife apart, but when I look closely, I can see a thin white bearing surface on either side of the blade in both knives. Looks like Teflon to me. Ergonomically and for me, I'm not sure which locking mechanism is easier to disengage when closing the knife. The liner lock on the T12 seems to be slightly more accessible in my clumsy hands but would wear on my thumb more with a lot of opening and closing. I spend very little time flicking my knives so this is not a problem for me. The push button lock/release mechanism on the E10 takes a bit more for me to get my thumb on but is smooth and easy to actuate. It also seems to be a solid long lasting design.
Not including the pocket clip, the overall thickness of the T12 is about .33". The E10 is about .375". So about a .040" difference. They feel and look thinner than that to me.
The larger, polished, stainless (I think) clip (cannot be moved on either knife) on the E10 comes from the end of the knife and allows for deeper carry in the pocket, which I like. Its design seems to allow for a bit smoother insertion in the pocket. Maybe because it has a bit more of a lead-in than the T12. The E10 is tip up carry which I like a bit more. The clip on the T12 is a nice looking anodized finish and is set up for tip down carry.
They both carry just fine for me and feel about the same in my pocket. As I said earlier, the E10 seems to go in and out of my pocket a bit more easily.
Every thing I've said about the E10 goes for the E6 also. The E6 is just smaller. I rotate through all of them, but if I could only keep just one, I would probably keep the E10. It seems a bit more modern and refined. But having said that, the T12 is just a very clean, smooth, simple design and I'm big on clean, simple designs that work. If you have no preference with the steel, then it is probably just a matter which design you prefer and your finances. I think I paid about $175 for my T12 years ago. The E10's are going for $300. Something to think about if the T12 you're looking at is in good condition and well priced.
Hope my overly wordy rambling helps. I probably didn't make it any easier for you to decide! Let us know which knife you choose. Thanks. Mike