A very wise choice--I congratulate you.
Whether the PSP or M8 (I have both) kind of depends on how you'll be carrying it and where.
The mag release on the M8 sticks out slightly and makes IWB carry uncomfortable for some people. It also is more prone to unintended magazine releases. The PSP is better in these two senses. Not everyone has either of these problems.
The M8 has a larger trigger guard, so it's easier to shoot with gloves. The American style mag release is faster to use, and as was noted above, is more consistent with what most people on this side of the lake are accustomed to.
The PSP has no heat guard above the trigger, and has a metal trigger--tends to get hotter, for some people uncomfortably so--during rapid fire.
Both versions have their devotees. Personally, I (slightly) prefer the PSP for carry. Both are among the best, if not THE best carry pistols. To argue in favor of one or the other is splitting hairs.
This design, in either version, is very near to indestructible, and given what the things cost, used P7's tend to have been well taken care of. A few things to check:
1. Pull out the firing pin and examine its housing for hairline cracks. This is one of the few components that has been reported to fail occasionally. Check the firing pin for corrosion--something also reported once in awhile.
2. Check the gas piston--the edges on the rings should be reasonably sharp. If the gun has been cleaned too aggresively (and not via the methods HK recommends) the rings may be rounded down, which will increase recoil.
3. Once every blue moon or so, someone reports extremely excessive recoil, which has been said to be tracked back to a cracked frame in the piston housing area. Try to shoot the gun you're interested in before purchase--and of course try to shoot a couple of other P7's to develop a baseline feel for how P7's shoot. Most people find all P7's to be among the lightest recoiling 9mm's extant. I've personally never seen a cracked frame on a P7, and I would rate this as among the most remote of possibilities.
Re the refurbs, HK did the work themselves, and other than the grind mark, these are usually reported as near or sometimes indistinguishable from new. They do NOT, however, come with HK's lifetime warranty, contrary to what is occasionally claimed--even if there's a blank warranty card in the box, HK is reported as not honoring warranty work. P7's rarely if ever need warranty work; but it's nice to the lifetime warranty.
For me, the main argument against the refurbs is that if you look around and are patient, you'll probably be able to find NIB or LNIB for not a great deal more money. I just bought a NIB PSP for $850. Last year I bought a NIB M8 for $800, and a NIB M13 for $1050. Refurbs are usually around $750, sometimes more. I've heard of prices as low as $500, and a bunch of people paid in the $650 range. For an extra hundred bucks or so--if you work at finding a great price--NIB with the warranty seems a better deal.
The only other issue of any note with the refurbs is that for some reason the white dots are said to work loose from the sights. This can be fixed with a touch of epoxy.
P7's of all varieties often have a brownish or purplish color cast to the slide--but not always. HK claims this results from chemical reactions between their bluing and the metal composition--I've heard that the zinc component of their alloy is the culprit. It's completely benign and indicates noting important about the gun, how it's been used, whether it was re-blued etc. I have no idea why only some guns demonstrate this--they tend to be older models. So maybe it develops over time, or maybe HK changed their bluing chemistry recently.
A few dealers claim that HK's quality control was better during the 80's than during the 90's--I've heard that some of the P7 cognoscenti prefer 80's guns as a result. I've personally never been able to detect any difference. The most recent p7's--I think only M8's, both new and refurbed--have some sort of disclaimer about guns being dangerous or something stamped on the slide. No one seems to like this. If you don't either, you'll want a something a couple of years old.
I believe only M8's were sold as refurbs.
Hope this is useful. I trust you'll love whatever model you end up with.
