I don't have a delay problem either.

I run a feigao 14xl on 8s lipo. It is in a savage, which is heavier than your buggy. The motor gets up to about 160f after a 25 min run. I use a pair of 4s 3600 lipos. They are 12c rated, so can put out about 45amps continuous. The lipos do warm up, but do not get hot, maybe 110 at the most.

This setup makes alot of power, more than a 8xl on 4s and maybe a little more than a 7xl on 4s. It runs much cooler too. I would recommend this setup, especially in a lighter vehicle. I think your 2500 batteries will be fine, even geared for 45mph.

I am using a great planes 60amps hv air esc. It has a bit of a soft start, but I can drive around it. It makes for a few wheelies, but not too bad. I have the turnigy hv esc that is going in my yusa rally, that car has a tekno clutch, so I will see how it performs. I will not have that car ready for a few weeks though.

I still say letting the motor spin all the time is bad. I can't explain why, it just feels like bad juju to me. I would trust aqwut's reccomendation on setting throttle trim to dial out the soft start, he's got a hobby shop worth of high end brushless setups, and more real world experience than most. Plus, he's from Canadia, Cananadans know their stuff.

But I dont understand what bad in that then motor spins slowly on idle when clutch not engaged? 15XL motor draw maximum 1.5A@noload and spinning freely on low throttle takes even less and maximum spins freely maybe 2-3% of hole run, just then you start run and slowing down to allmost dead stop, thats it! On Helis motor spins on 80% trottle all the time until battery dump, nothing happening :)
I dont understand how I can dial out throttle to eliminate soft start? Maybe we speak same but understand difrently? Maybe he doing same dialing throttle to 40% then motor start spin and on ground it not move? Did you ever played with this ESC? I do last week on (6S version), tried different ways settings and etc just no luck. It responds immediatly only then motor spins. I have opposite feelings :) that this may work. And anyway I will buy MMM for truggy and current MM will be unused, anytime i can go to 4S.
If "HV project" starts I will inform

spinning without the clutch engaged would be a no load situation, and motors heat up very fast with no load, as all the excess energy is disipated as heat, also, having current constantly flowing through an esc just sounds bad to me. If they are passing current they are meant to be moving for cooling airflow. Thethrottle trim is basically the same idea as yours, just without the motor spinning. Adjust it until the motor just starts to spin, then back off 1 percent so the motor does not spin at neutral.

I have set it as forward as I can without the motor spinning and the problem is still terrible. Yes I set the throttle range. Me and my bro both have one in seperate cars, and have both tried all kinds of weird and wonderful methods of getting rid of the delay and cant manage too... Maybe theres different kinds of software on them or something? I'll have to get a vid and try and demonstrate what I mean.