Can you find a local range where they'll rent one to you to try?
The 340/360PD models have titanium cylinders. This restricts the Magnum loads used to bullet weights of not less than 120gr to help reduce the possibility of premature erosion in the titanium cylinders (gas erosion in the charge hole throats, cylinder face, etc).
S&W also warns that ammunition which is going to be used in their Ti, Sc & PD revolvers needs to be checked to make sure it doesn't exhibit signs of the bullets becoming unseated by recoil (see page 12 of their revolver manual for modern style revolvers
http://www.smith-wesson.com/wcsstore/SmWesson2/upload/other/S&W_Revolver_Manual_01-30-2011.pdf ).
Now, the M&P 340/360 differs from the PD models in some ways, one of which is they use a PVD coated (black) stainless steel cylinder, instead of titanium. That adds a little bit of weight to the guns, but when I bought my first M&P 340 (I own 2) I checked a number of Magnum loads for signs of bullets coming unseated, anyway. I found some Magnum brands/loads which exhibited bullet pull (unseating) and some which didn't ... when
I was shooting.
I mostly carry +P loads in my M&P 340. Why? Because that's what I carry in my 642-1's that are rated for a steady diet of +P, as well as in an older steel-framed 649 (although it sees mostly standard pressure rounds for practice, with only occasional use of +P for function check, continued familiarization and carry use). I prefer the balance of controllability & recoil management I can wring from the +P loads I use. Sure, I've demonstrated in practice & quals that I can do well with Magnum loads, even doing rapid doubles & triples in some demanding qual courses-of-fire ... but I can do it just as accurately, and even faster & more controllably when using +P loads.
The Magnum loads in the M&P 340 develops substantially heavier recoil than +P loads (which generally develop more felt recoil than standard pressure loads). Is it too much? Dunno. That would depend on the individual shooting the gun & loads at any given time.
I tend to think the even lighter 340/360 models with the titanium cylinders develop even more felt recoil than my M&P 340's, based upon
my experiences and perceptions when shooting Magnum loads in PD models. (I was shooting 125gr Magnum loads in the last Ti/Sc Magnum J I used on the range.)
Recoil force is real, but how it's perceived, meaning
felt recoil, is a pretty subjective thing can vary among folks. It's not uncommon for folks to describe they feel more recoil directed into the palm/web of their hand with heavier bullet weights than lighter bullet weights, though. For example, the 125gr Magnum loads may generate more muzzle blast and whip, but the 158gr Magnum loads usually kick harder against a shooter's palm/hand. I've found some 135gr & 145gr Magnum loads that were somewhat of a 'compromise' for me when it came to felt recoil and muzzle blast. I still wouldn't call them a "fun" experience, though.
I've seen some folks experience injury to their thumb from not having it properly positioned (the rear of the cylinder or the cylinder latch cut their thumbs under recoil). It also pays to be mindful of the barrel/cylinder gap and the danger of hot gasses (or bullet fragments shaved off). There's a reason they put that steel insert above the B/C gap in the aluminum Sc Magnums.
Personally, I tend to 'feel' pain to the bottom of my index finger's last knuckle, caused by the trigger guard rising and hitting it under recoil, whether I'm shooting +P or Magnum loads. I just feel it sooner when shooting Magnum loads. (And I'm a long time Magnum revolver shooter who used to think an enjoyable afternoon was one where I fired a few hundred rounds of .357, .41 or .44 Magnum through medium & large framed revolvers.
)
You really need to try one, if possible, with whatever factory ammunition you anticipate using ... which meets the requirements contained in the safety warnings in the user's manual, as well as whatever range policies & restrictions may exist ... and decide for yourself.