Alfred, I don't own an Axis SS MM90 but since nobody chimed in, I thought I'd at least reply with a few thoughts on the Valentine:
They are incredible guitars. Tonewise some say the bridge pickup is somewhere between a tele bridge pup and a P-90 and I would agree. I have a new Yamaha Revstar Standard with P-90s (takes care of my 24 3/4 scale Les Paul/SG urges-- very fun guitar to play) and I do love the sounds I can get from P-90's so I would imagine your Axis can give you some awesome tones. I almost bought a BFR Ghost in the Shell Albert Lee this past week, but the particular guitar I was looking into weighed a ton and I had to pass on it.
But back to the Valentine, it's a lot like a Telecaster in terms of feel and tone- the bridge pup is thinner, brighter and twangier than a P-90, but that neck humbucker is very Gibson-like-- depending on what you do with the tone knob. And when you split the neck, it's not going to sound like a Strat neck, but it's a very usable tone either on it's own or combined with the bridge. The active boost is something I use every time I play.
I'm not good with describing neck profiles-- I did play an Axis in a shop a few months ago. I liked the neck on it a lot. It didn't feel terribly different on a "feel" level to the way my Valentine necks feel-- despite maybe they have vastly different profiles on a technical level. I don't know. I have hands on the bigger side and both necks feel great to my hands. I didn't buy my Valentines to "shred" on but if I want, I can even shred on them maybe a little better than on my "shredder" axes. Haha.
It's kind weird when I look at both body styles-- if I just kinda reimagine the upper horn on the Valentine as a single cut type thing, they'd have almost the same body yet in reality I see single-cut and double-cut guitars as different beasts for some reason--when really its just mostly aesthetics.
There's a good reason the Valentine gets high reviews. It's an extremely versatile, well-built, thoughtfully designed instrument with some very useful features and a modern yet classic style to boot. I always want to grab it and play it and never want to put it down. I think if you're used to playing a P-90 instrument, then the Valentine should give you plenty of new tonal options while having a bit of familiarity too.
Cheers,
Ted