Replacement Mic for PD170
 

I'm looking for a replacement for the stock mic on my PD170. I already have a ME66 but I'm looking for a mic closer to what the stock one does. Would the Sennheiser ME64 be the one? Any suggestions?

What is the pattern on the stock mic?

As stock camera mics go, the ones that come on the 150/170/390 and the plastic-cased version on the PD-x10 are far from the worst available. They are far from the best too of course but any camera mounted mic is already handicapped.
The pattern of the stock mic would probably fall between the ME64 and ME66. The ME65 is a hypercardioid, but it's intended for hand-held vocal use, not in the same category as the progression from ME62 up to ME67.
If you want to stick with a smaller hypercardioid mic that's under $200, then there's really only two choices. The AT873r or an Oktava MK-012 with a hypercardioid capsule from the SoundRoom.
The Oktava has better self-noise, but the AT873r is a little less expensive and much more practical for camera mounting.
If you wanted to go more expensive than this, the AT4053a hypercardioid, an AKG Blue Line hyper and preamp or a AT4073a short shotgun are very good. The Sanken CS-1 is also good but a little more expensive still.
If you want to stick with the wider pattern of a cardioid, then you could get an ME64 to go with your K6, or you could get an AT3031. If you routinely work in quiet environments, the 64 would be hotter. If you work more in loud environments, the 3031 is tough to beat for max SPL and moderately high sensitivity with very low noise.