Did you take the Audition of Benq and Epson side by side ?
No, unfortunately those trials were days apart for Benq TK800, Optoma UHD30, Optoma Hd30hdr.
Didn't even get a trial for Epson 7100, just pulled the trigger as others won't fit in my room.
For me also it boiled down to Optoma 30HDHDR/Epson7100/Benq TK800M..
How much will the difference in pic will be betwen true 4K Vs Enhanced 4K Pic ..Is it really noticeable...
How much difference in pic quality will be between Optoma HD HDR30 Vs Epson 7100 from 12 feet distance ?
Frankly, I couldn't notice a difference between these three. Again, it was observed days apart, so don't consider it seriously. And, although I've good memory, it's not photographic .
I had requested to play 4k and full hd content. Benq was projected from 12 feet distance on 100 inch screen. Sitting position was directly below the projector. Didn't notice any real difference in 4K and FHD content in that setup.
The Optomas were tried in a different setup on Accousticaly transparent screen (150 inch screen probably). Projection was from beyond 14-16 feet range and sitting position was around at 12-14 feet . I could get the difference between brightness, but not in resolution (4k vs FHD for same projectors) .
In all these DLP projectors, I couldn't notice any rainbow effect. I didn't ask them to run any tests which typically expose that, as I was primarily focused on audio part at the time.
I was still wary of the same, during my projector hunt phase, considering I didn't take my kids / better half or parents to try these projectors. What if, I buy this and any of family member is prone to "have a good eyesight" to catch it? . It would have ruined the whole HT! Even with bad eyesight like me, I didn't test it for those corner cases; if I had happened to start seeing it post purchase, it would have meant an unwarranted upgrade, soon! I wouldn't be able to unsee it, every time it's on.
I would have made that purchase in any case considering my budget though. But, projection ratio and absence of lense shift was a deal breaker . Had to increase my budget from Optoma Hd30hdr to Epson 7100. And man, I'm happy to go that way!
As far as the heating and projector placement issue that you have, I didn't have it. As my window is 9-10 feet behind the projector in another step up room, just behind the 16/18 feet long room.
I'm sure, you've also considered Mi UST laser projector as well. I had considered it, ditched it for absence of 3D and wildest "fan boy" vs "ultra disillusioned" reviews. One would think of consistency in those luxury expenses... right?