(As I say about all Macs) - These are neat machines!
A lot of information about them is availalbe here:
http://www.kan.org/6100/
The 6116 looks like it would have started with one of the higher end configs. You can run anything from 7.5.1 (there's a small chance the 7.1.2 install from a 6100/60 would work too) up to 9.1 on them, although you'll want more RAM for 9.1 to be even a little bit comfortable. 8.1 or this may be a rare case where 8.6 might be worth looking at - because you'll get a lot more PPC code, which will be good for a 601 (versus running things in 68k emulation) but still a lower memory usage than 9.1 (supposedly, TBH resources on a stock or near-stock 6100 are typically slim enough I'd suggest looking at 7.6.1 or 8.1.)
It's pretty ho-hum, it was the mainstream business desktop when the Power Macintosh family launched in 1994, so it supports up to 832x624 displays on the onboard graphics, and up to 1152x870 at 24-bit/full color if you put in an upgradeable high performance video card from a 7100 or 8100.
What kind of stuff do you like? It's a reasonably competent tourism machne if you just want to look at MacOS, ClarisWorks, HyperCard, and Oregon Trail. It should be ~ok~ at 68k and early PPC gaming. A solid quadra is going to be faster than it at almost anything "68k" but that doesn't make it a bad machine per se.
If you like hot-rodding there's the aforementioned HPV video cards, a DOS card, a nubus adapter and also G3 upgrades, with various combinations available. People were using these as dailies into the early 2000s with these kinds of upgrades.
If you prefer "not very upgraded" but "not too upgraded" but "not too not upgraded" you could look into what cache yours has (none stock, there are apparently 256k, 512k, and 1m modules) or can have added and then look into getting the HPV a/v or graphics cards, which will make the system feel very sprightly. Add in some RAM and you have something that'll probably even benefit from the extra speed of a SCSI2SD v6, over a v5. (I've been meaning to test effective v5/v6 speeds on mine.)