Consider that Montage, thanks to its more complex synth engine, is capable of producing more rich and articulated timbres.

If your goal is to use just the same old timbres such as piano, strings, brass and the like, remain with your MOXF.

How do you want to measure the difference? All 741MB of the Motif XF/MOXF Wave ROM is included in MONTAGE plus almost 5GB of data you’ve never encountered. All 7981 Arpeggio plus a couple thousand new ones. In the MOXF you had 9 Preset Banks (1152) and 3 User Banks (384)... MONTAGE currently has well over 2000 Presets and 5 User Banks (640) So the upgrade is huge.

The MOXF was considered a Music Production Synth because it had a MIDI Sequencer integrated with the tone generator.
The MONTAGE is a Music Synthesizer combine AWM2 sample playback with FM-X synthesis.

If you have a favorite VOICE in your MOXF... find it in the MONTAGE and play it... your ears will tell you everything you need to know!

The AWM2 portion of MOXF and Montage are highly related. MOXF has all of the preset performances that the Motif XF has -- and Montage doesn't reproduce those performances (although you could manually create all of them one-by-one on Montage given you have a Motif XF or MOXF as reference). Instead of those performances - you have new ones in Montage to showcase the new control paradigm in Montage and also to break away from legacy.

Although you do not care about the new "technology" - I assume this perhaps means motion control and other "gizmo doo-dads" - this "technology" has a direct impact on the sound since you can program parameters that affect the sound in ways you could not do in Motif XF/MOXF. If this is better or not is a matter of opinion. "Bang for your buck" sometimes comes to play and everyone has a different "cutoff" point. MOXF is going to be less than half in price (retail) than a Montage. YMMV.

Many of the raw sonic improvements of the Montage I hear clearly in the studio - and not as clearly running through sub-standard setups at gigs where I'm always only afforded a mono feed. So for the AWM2 side - ignoring motion control - a MOXF would sound very similar for the sounds I generally use. Most of what I've done in the band setting could have been accomplished with the previous tech. I do use Montage's FM-X engine which is a whole other you-can't-get-there-from-here thing when looking at MOXF. MOXF has sampled FM - but you can't do many things (sound-wise) on MOXF that you can do with FM-X in Montage.

Also, the keybed of the MOXF8 and Montage 8 are different. I hate-hate the MOXF8's keybed. It's too mushy and sluggish for me. This is completely personal preference - some love the MOXF8's keybed. To me - the "feel" translates into the "sound" too - because I'm fooled into hearing certain things when the keybed responds well to what I expect/want/like. A bad feel - to me - makes a keyboard sound worse even though there will be no real difference to the audience if you switch out the keybed except for how the "touch" may be different -- I'm saying assuming the touch is the same between the two keybeds.