most of what i read is rather negative about LGP undercarriage, mostly about more u/c wear with the wider shoes etc..
-are there any benefits to wider shoes other than lower ground pressure to work in soft,swampy ground?

- currently have the 30" shoes and have been thinking of trimming them down to the standard 24" shoe (D6c)
-have no intentions of operating in swamps...

is it a good idea or bad idea? interested in your thoughts and experiences, thanks

I have no direct experience with your lgp d6 but I did run a d3b lgp. I ran a d6d and wouldn't consider a d6 a swamp machine. If you're going to be using it as a general purpose dozer I would cut them down. The problem comes when you get in uneven terrain which can put a lot of pressure on the outside edge of the track pads. Stumps and rocks and such is where the increased wear comes in. I will say the d3 lgp machine was a dream to run but was just used for finish work and pushing swamp type dirt

yes that's what i was meaning Gary, general purpose dozer, just stump jumping

The standard track shoe for the D6C or D6D LGP is 36". The 30" pads were intended to reduce wear when flotation was not needed as much. The extra wear to the undercarriage from operating in dry conditions is caused not only by the width of the track pads but also buy the extra length of the roller frames/tracks.
Trimming the pads is a bigger project than you think, unless the undercarriage in really great condition I don't know if any gain you would achieve would be worth the effort of the trim job.
The easy fix is to adjust your operating procedure to avoid sharp turns and rough terrain until it's time to replace tracks. 
The wider pads are nice for snow. You might regret the trim in winter.
Craig

isn't the grouser bar height on the lgp pads lower than standard pads? if you trim it might affect traction???

not sure how i would get 36" shoes to fit and clear everything, it's already tight confines..
-yes it's a big job for how much benefit, that's the dilemma...is it really worth the time and trouble...?

Okay, I thought you were talking about 30" pads on a D6C LGP machine, 30" pads on a standard D6C would be maxed-out.
Still a tough call as to weather the potential gain is worth the effort.
Craig
 

and what would be the most cost/time efficient way to cut shoes?
-oxy-acetylene
-big plasma cutter
-mechanical band saw of some kind
-other?

cost wise I would go with a good old-fashioned oxy-fuel setup. if fire risk was a concern you could try a good quality zip cut in a grinder. I feel you would need a good-sized plasma cutter ( they always cut less than they claim) but if one already has one that would work fine I would say away from a bandsaw and you'll be cutting good steel not just mild steel and well blades might not last long plus cutting time would be longer and it would be hard to lube-keep the blade cool on a bandsaw.

I have attached a screen shot from the 6th edition of the performance handbook showing the different undercarriage options that the D6C had for show width.  Considering it does not even list a 30” pad option for the standard gauge tractor, I wonder if a: someone put them on themselves to try and make “homemade” LGP tractor, or b: if Cat later offered it as a wider pad.
The standard gauge D6C is 74” and the standard pad width as you can see by this chart was 18”.  And had optional widths up to 24”
The LGP gauge D6C is 83” with a track pad width of 36”.  That means the track frames were spaced out an additional 4.5” on each side to allow the wider pads for better floatation. 
If you truly want to narrow your track pads I wouldn’t go any narrower than 24” personally, you never know when you might be in a situation where that little extra width gets you out of a bind.  You can see that a standard gauge D6C with the 18” pads has almost double the ground pressure as the full LGP gauge tractor.  So you do gain floatation as the pads get wider.  
I think the best option for cutting them is oxy/acetylene, just give yourself a nice straight edge to follow and cut equal amounts off each side of the pad.  Don’t just cut off one side like I’ve seen others do, otherwise you still have the same problem on the original width side of the pad.
Yes wide pads can cause premature wear in undercarriage because of the extra stress that can be added by hard uneven terrain.  What kind of work do you plan to do? How often will you be in softer conditions? Are you working in lots of big rock? These are the questions I’d consider before cutting to narrow.
The other option is you could watch for a set of narrower pads to come up for sale and swap the pads out rather than torch cutting them and potentially weakening the metallurgy of the steel from the heating and cooling process.
Hope this is of something use, 
Nathan