That is a great fucking description. I agree with and understand this completely
I’ve never played a mark IV, but I’m fairly certain I’d dig it more than my c+ lol.
This is the same for me except I like that sweet spot between clean and OD, more sustain but not much gain, and loud enough that I don't have to dig in so hard and I can use a lighter touch with my picking hand for leads. It's demanding still because all your mistakes are basically front and kenter.
I tend to hunt for that a lot, when playing a strat or tele. A nice singing lower gain sound, that feels like high gain, especially playing leads.
I'm chasing that with humbuckers and a Twin. A smooth, creamy lead sound without being too gainy. If it gets too gainy then I feel like I'm doing a rock music solo. It's elusive at times since a lot of live work is all moments notice volume knob adjustments.
The xtc is great for sure, but I'd switch out the lead channel for a mark series lead channel though, but the xtc has the cleans and crunch I like.
I did a gig recently accompanying an acoustic player, where I was trying to sit in that sweet spot. The clean channel of my mark V, blue (bluesbreaker) side of a browne protein, a little bucket delay in the loop, and the center pickup position on my tele seemed to do the trick; riding the volume & tone controls a lot, and trying to pick very lightly for the most part. Always felt like I was riding that line gain-wise between overpowering & getting lost.
A PAF type humbucker might be your ticket. I mostly have used Seth Lovers and my preferred 57 classics the past six or seven years. The 490 is good to. I would think it would be worth a try to set whatever too-hot pickups you have way down in the rings just to see what happens. They might give you exactly what you are seeking cause you can definitely tame output by reducing proximity, assuming you have enough adjustment range in the rout and screws.
I recently put a set of Thornbuckers into one of my guitars, even though the EQ curve and output specs are comparable to a PAF style, they're fire breathers sound & feel-wise. I like them, just not what I'd want in that context.
For what it's worth I just like the 57's better and I used the Seth's in my main player ES copy for maybe 100 gigs. Smoother top end, richer, and what feels to me in real world use like a little more output. I'm using a Twin which has pretty good clarity so if you are using an amp (or guitar) with a different perhaps darker voicing the Seths may be ideal. They have more clarity and a bit more aggressive bite on top but for me a bit more shrill in the high end through my rig. I tested them in two Edwards, an ES and an LP.