There was a thread a bit ago asking some questions about running the SCT Combo (MMP and 2400kV) on 4S and I have some findings to report. I have just gone 4S (35C 4500mah) with my Slash-Pede 4x4 MT and had it geared 17 / 54 with pro-line trencher tires. The slash chassis is 1.75 in longer and a couple oz heavier (due to extra length and larger body) than a 4x4 pede, but is otherwise the same truck for reference.
After running several packs I found the peak temp to be around 160F ~ 170F, the MMP fan would start and run after about 1 minute and stay running as long as I kept driving, but would turn off after about 30 seconds of stopping. This was through tall thick yard grass, goning up and down hills, and doing some speed runs on the pavement.
I also found a warehouse building nearby that's about a 100 meters long with rough asphalt that has some nice little hills and what not, but also a straight away running the length of the building. Its very high traction with those trenchers (about as high traction as you can get). I hammered the truck the entire pack, running full throttle (or as close as I could get without entirely loosing control), would turn around and do it again and again until the LVC stopped my fun. Hit 199F~200F at the end of the pack. Slipper is set to act almost like the launch control feature on the MMP so it slips just enough that it usually doesn't pull a wheelie from a dead stop (although once going about 20mph it will wheelie on demand if I blip the throttle or hit a bump). Run time was about 20~25 minute range, outside was dry and ambient temp was about 65F.
I'm going to say that 16 / 54 is about max safe gearing for this combo, 17 / 54 is a bit over geared and can be done if care is taken (cold weather or shorter run times), but for bashing or hard long racing I would suggest not going over 16 / 54. I have not even tested that gearing yet, but one tooth should be enough to give me a bit of a safety margin to keep it under 200F in the most extreme use and it is also what the castle gearing chart stated as max recommended for the 2400kV on 4S in a slash 4x4, at least the booklet that came with my SCT combo.
Also note that castles revised version in .pdf now states 14t / 54 as max instead of the 16t / 54 my booklet did, but I'm guessing that's with a 10 deg timing advance. I'm running 0 advance which is equivalent to dropping 2 teeth, so I am still within their guidelines. If I'm not mistaken this is also what Thomas-P ran in his 4x4 Pede before he went to the Hobby Wing motor (although I don't know if he ran 0 advance or left it on the default 10).
I hope this helps anyone looking to run their SCT on 4S! Any additional thoughts, comments or experiences are always appreciated so feel free.