@Meanadidas
If I had to only have one, it would be in this order:
Mk2 Impact, Maverick, M3.
Tbh, M3 was really hyped up by some of the big names out there but I have yet to be WOW'd by mine. I've seen a few M3's get posted for sale the last couple days...for a new model, that says something.
Well, I don't think that you can read that much into the sales of M3's (says the guy who is in the process of selling his second M3 since purchased in April):
1) A lot of folks, myself included, bought our M3's when they first became available since FX is not well known for being able to supply their guns in the quantities necessary to support the market;
2) Whether right or wrong (I tend to think wrong), the release of the M3 severely impacted the 'value' of MkII's on the used market;
3) Therefore, with a good working MkII in hand, the M3 was found to be a little redundant in the collection. And since it had the good 'used' value, this is what I have been selling.
4) I have further found that for me, the Impact (be it MkI, MkII or MkIII) may not be the best suited rifle for the shooting I do. I absolutely love the Impact Compacts for squirreling at the range, but I don't shoot my longer Impacts as well at distance as I do my traditionally stocked rifles. And the longer Impacts are just not as handy to carry when I am walking and stalking at the range.
5) I don't compete and I am not a dyed-in-the-wool tinkerer - I set up my guns for a preferred pellet and velocity and generally just leave them there when I get a harmonic tune and the accuracy I want.
6) I have owned a Maverick. It just didn't work all that well for me as a shooter. It also liked to dump its air mid-way through a shot string. I sent if back for refund, and have never looked back.
I agree with you that a MkII is a fantastic gun. Knowing what I know now regarding the differences between the MkII and M3, I likely wouldn't have bought the M3's IF I could have found a good used MkII at a more reasonable price than they currently seem to be selling for.
But I also think that FX saw the trend towards shooters wanting to sling slugs (personally, I haven't bought into slugs significantly yet, and for my needs pellets are shot 95%+ of the time). I believe that FX has optimized the M3 to be better adaptable to shooting slugs well, which the OP wants to do. Larger plenum (but not as large as the Maverick), and possibly enhanced internals (larger valving, air channels) for slug shooting.
All things being equal and available, I would rate the M3 in first place, followed pretty closely by a good MkII (for the right price), with the Maverick bringing up the rear (NOTED however that MY experience with MY Maverick was not a good one.)
