Update 30/06/2020 4:56 am PT: VideoCardz confirmed our suspicions that the chip pictured by TecLab was not a real Ryzen 5 3600XT, but rather a standard 3600, making this a likely case of a fake preview.
If it were real, why would anyone cover the "XT" part of the product name with tape? That makes zero sense and removes any believability that it might be a real 3600 XT in the photo. Covering the serial number and QR code makes sense, but not the one part of the product name that would identify it as a new processor.
In any case, I wouldn't be all that surprised if they were to get access to a 3600 XT, seeing as the processor is set to launch in a matter of days, and there are likely not only chips in reviewers hands at this point, but also making their way to retailers and system manufacturers. It seems a bit pointless leaking performance numbers with only days remaining though.
Logically, I suspect performance is only going to be a little faster than a 3600X, which is in turn only slightly faster than a 3600. There are still some unknowns in terms of what multi-core boost clocks will be like though, as no specifics have been announced about that yet, and it's possible that the chip could potentially do a better job maintaining higher boost clocks in general.
But is this default setup of the 3600XT or PBO ?
Another thing to ask would be if the 10400 were running at stock memory settings or not. Most people buying one of these sub-$200 locked i5s are likely to pair them with a mid-range B or H-series motherboard, but Intel artificially restricts memory speed on those boards to DDR4-2666. Running an i5-10400 with memory at that speed can cut gaming performance by around 5-10% in CPU-limited scenarios compared to DDR4-3200, so test results utilizing faster memory are not going to be entirely representative of what performance will be like on most systems running that processor.