To my best knowledge K6+ is the collective term for K6-2+ and K6-3+, and all K5, K6, K6-2, K6-2+, K6-3, K6-3+ have unlocked multiplier. With K6+ you can use setmul to change the multiplier and turn on/off the caches on the fly. I had a bunch of embedded K6-3+ and I didn't notice any functional difference from the mobile version.

The Mobile versions have higher case temperature ratings.
There is no form/fit or functional difference.
If you are an extreme overclocker a Mobile would be preferred but no one else would notice a difference.

Embedded versions come in several different packages that usually must be soldered onto the mobo.
They are a no-go for a consumer mobo. (Without a huge amount of work anyway.)
They produced the Embedded for a very long time after they stopped making the standard version.
Most likely had a use in industrial automation. (CNC machines, assembly line robots and so forth.)

Good places for info. (The regular wikipedia is often AFU on this topic.)
https://en.wikichip.org/wiki/amd/k6
https://en.wikichip.org/wiki/amd/k6-2
https://en.wikichip.org/wiki/amd/k6-iii
http://www.cpu-world.com/CPUs/K6/TYPE-Desktop%20K6.html (see pic)

Things to check when choosing one. (Make sure mobo supports it.)
The Vcore and I/O voltages change quite a bit between models.
They have some odd ones for the FSB. For example one that does 95 MHz but not 100 MHz.
.

The last 3 characters tells you the package, the core voltage, and the maximum tolerable temperature in Celsius.
First character:
A - PGA 321 aka Socket 7 (PGA 296 aka Socket 5 on K5)
B - BGA 360
I - BGA 349

Second character:
U - 1.5V
T - 1.6V
P - 1.7V (3.3V on K6)
N - 1.8V (3.2V on K6)
M - 1.9V
C - 2.0V
D - 2.1V
F - 2.2V
G - 2.3V
H - 2.4V
L - 2.9V
B - 3.5V

Third character:
Q - 60
X - 65
R - 70
Z - 85

So the only difference between ACZ and ACR is the temperature ceiling. Theoretically an embedded socket 7 CPU might be damaged from unprofessional desoldering work if the CPU was soldered on the board, but I haven't seen or heard anything like that.
Sometimes there is a fourth character (e.g. ACZM) that I haven't cracked the meaning of.
K5 has an I/O voltage requirement of 3.5V and anything above that requires 3.3V.
I wouldn't worry about odd bus speeds such as 95MHz or 97MHz. Anything I have/had above K6-200 would run at 100MHz bus, even the ones rated for 66MHz bus.

Cga.8086 wrote:

should i just find an K6-III+ and forget about the k6-2+

As PCBONEZ mentioned, first make sure your board has BIOS support available for the "+" CPUs. They weren't originally intended for desktop boards, so often this requires using a Beta BIOS or 3rd party hacked BIOS. There's a site somewhere that has a long list of which boards have "+" compatible BIOSes available.

But if it will work, then either of these are great CPUs. The K6-3+ is slightly faster but it's only a small difference. The K6-2+ is much more common on eBay and cheaper, so unless you really want to max out the board, the 2+ is fine.
Either will typically clock into the ~550MHz range easily. Above that you start having to flog it. A conservatively overclocked K6-2+ will outperform any original K6-3, and is barely any slower than the K6-3+ at the same clock.

You'll want the board to have Vcore settings of 2.0V or less. AMD's datasheets for these chips warn against anything in excess of the intended range over the long term (I'm not sure how much to take that seriously), but additionally they list 2.2V as the absolute maximum (and I do take that seriously). This means that even a jumper setting of 2.1V might be slightly risky due to imprecision and transients.
Your board might have undocumented voltage settings. Mine for example goes down to 1.3V, but the board manufacturer only listed the options they thought were relevant at the time of manufacture.

All K6 chips are unlocked, but only the "+" chips can change speeds on the fly.

Hey, PCBONEZ. Haven't seen you around in a while.