I was in a similar upgrade situation. Had a Mist 3800 DLP for 7 years, served me really well. Thought I had it dialed it pretty good for its capabilities.
I was also running a very small screen (small room)---80" diagonal 16:9 .9 greyscreen, which was intended to match the Mits 3800, which it seemed to.
Was looking at used JVC's and/or B-stock, etc. Only B-stock models were the newish light cannon models, which even with the iris clamped all the way down, would probably still be too bright for my 80" screen. Ultimately I thought they'd be too bright at worst or unnecessary at least--in my set up.
After doing much research, I decided my used JVC target was a RS46 at the low end, but really was shooting for the DI models, RS4910/RS49/X500, budget around $2k. I ended up getting super lucky and snagged a low hr used RS57 (X700) for that target price, and it came with a new in box extra OEM lamp. I think this RS57 was the perfect fit for my small room and small screen. With the manual iris at -12 and DI @ Auto 2, the brightness is about the same as my outgoing Mits 3800 (about 1,000hrs on the Mits Lamp and 600 hrs on the JVC Lamp).
On bright scene, or mixed bright leaning scene content, these PJ's are about the same, perhaps slight edge to the Mits.
Of course blacks are incredible on the RS57 and shadow content is very black with little to no haze compared to the 3800. So no comparison when it comes to blacks here. Interestingly both PJ's have about the same shadow detail performance.
I wrote up a long side by side comparison here> *Unofficial* Mitsubishi HC3800 Thread
And you can read the rest of the page that post was on here> *Unofficial* Mitsubishi HC3800 Thread