I can only speak anecdotally on this. But the 6200 appears to be a half mask.
https://www.3mcanada.ca/3M/en_CA/company-ca/all-3m-products/~/3M-Half-Facepiece-Resuable-Respirator-6200-medium-24-case/?N=5002385+3293806388&rt=rud
The 8511 is a fabric respirator
https://www.3mcanada.ca/3M/en_CA/company-ca/all-3m-products/~/3M-Particulate-Respirator-8511-N95/?N=5002385+3293789676&rt=rud
We use both extensively. However, in purchasing, i prefer the half masks as after you pay the initial upset cost for the half mask itself, the filters can be removed/replaced and used for a longer period. So you save in the long run. Whilst the 8511 are disposable, and you go through the masks significantly faster. Its good to have both in my experience. But if you're looking at long term cost..the half mask is a better option. Also, you can get different filter media for the 6200. We often just get P100 filters in bulk and call it a day. They do more then the typical N95.
The downside of the 6200....you look like a bit of a doofus walking around compared to the 8511. 🙂
Just my two cents.
https://www.internationalpreppersnetwork.net/viewtopic.php?f=57&t=7738