The LP S is a very nice cartridge. It does have a hint of warmth. This is very evident when compared to more neutral cartridges. As I state this, it is important to know that the LP S has many other characteristics that set it apart for other cartridges that are possibly considered more neutral. Having said all that, I could own and would not mind having an LP S in my cartridge collection. Not at all...
But! The SLR Gullwing is the cartridge that has most of my curiosity. Additionally, it is most likely the cartridge I would want to own over the long haul. The construction is mostly that of the LP S without the wood body. Lucascheck, rightfully so, says the LP S is the better cartridge. However, there is a bit of extra warmth I've observed in the 5 or so systems where I've personally setup the cartridge, including my own. I have a sneaking suspicion I'd prefer the SLR Gullwing by a hair. I would speculate the SLR Gullwing will loose some of that smidgen of warmth, which is very beautiful and slightly softens transients while giving all music a very slightly warm glow. This personal preference of mine or anyone elses should have no major bearing on your decision because we dont have to live with your selection you do. Make sure your choice is what you want and not anyone elses.
The individuals I know that own the LP S are extremely happy with it and they should be. Two of the owners, I personally recommended the LP S cartridge to over others that would catch the favor of many due to the name of those cartridges alone, are not second guessing their decision.
The Benz cartridges do extremely well at trackability, as they have in the past. The addition of the new micro-ridge stylus improves all of the Benz S class cartridges (including LP S as well as the SLR Gullwing) in the area I had always felt they could use improvement - Traceability. The new S class cartridges have very respectable traceability.
You have a tough choice ahead of you but the choice is among two excellent cartridges. The task for you is to get a handle on your current setup and decide if the additional warmth of the LP S will be an issue for you. This added warmth of the LP S is not overly noticeable but it is there.
Both cartridges should be more than capable of providing excellent sound that will keep you satisfied for some time to come. Additionally, your arm is a design that will allow both cartridges to mate and perform well.
Dre