The Great Wyrm is a Chaotic Evil Colossal dragon, while the Elder Red is an Evil Huge natural magical beast (dragon). The Wyrm has an initiative +2 (seriously?) and a Perception of +38, while the Elder has an Ini of +18, and Perc +19. Once again, the numbers in the MV are much more linear and samey. The Elder Red seems to be much faster as far as initiative is concerned.
The Wyrm has an AC of 39 and 449 HP, the Elder has an AC of 38 (surprising how AC is very similar across the versions) and has 832 HP! Big change! Being an Epic monster and being a Solo (and a Soldier) means that the Elder Red gets a huge boost in HP compared to "normal" creatures of its level (the lvl 22 Lich Soulreaver has only 156 HP!).
The Wyrm's saves are +25, +14, +24. The Elder's Defenses are 36, 33, 32 (+26, +23, +22). The Wyrm has resistance 20/magic and is immune to fire, paralysis and sleep. It's also vulnerable to cold and has a fire aura 1d6. The Elder has only a 20 resistance to fire. Again, the PF monsters are much much heavier on various defenses.
With a move the Wyrm walks 40ft. (8 squares) and flies 250ft. (50 squares), while the Elder walks 8 and flies 10.
The Wyrm can make 6 attacks in a round: bite +37 (4d8+24), 2 claws +37 (4d6+16), 2 wings +35 (2d8+8), tail slap +35 (4d6+24). Assuming 50% success chance that's something like 87 dmg average. It can also breathe fire for 24d10 (~66 damage, if you fail your save, so probably more like 33 or even less, because lots of characters have protection from fire, uncanny dodge and so on at that point) every 1d4 rounds. What I get from this is that the Wyrm is (at least in theory) much better off making full attacks each round, and would use his breath only to finish off groups of weaker foes.
The Elder's attack math is a lot more complicated. On a count of its Initiative+10 it can attack with two claws or a bite, unless it's stunned or something, in which case it shakes off that effect. Then it can bite, claw twice, immolate one foe or breathe fire on its turn (the immolate and breath need to recharge (and have roughly a 33% chance of recharging each round). Plus it can make immediate interrupt attacks with its tail when enemies move close to it. So in the very best situation it will probably make two claw attacks (2x3d10+14), use its breath weapon (4d12+17) and tail strike at least once (2d8+4), dealing something like expected 59 damage per round, but in the theoretical worst case scenario it will only make a bite (2d10+6) doing something like 9dmg per round. So, all in all, I'd say you'd expect ~34 dmg per round from the Elder Red. But this math is problematic because there are so many factors to be considered in it. There's also the fact that Immolation and Bite also do ongoing fire damage if they hit, until the target saves, so that's an extra ~30 possible fire damage per round. Now, while that's still less than what the Wyrm can do, I think the Elder is comparatively dangerous because it can theoretically do more different things each round, its tail sweep also knocks enemies prone and is a big tactical advantage. The Elder also has two action points, which means it can take an extra action twice per encounter, once per round.
-the -10 to Defenses is still valid
-the MV monster has a lot more HP than the PF one (almost twice as much) but it has a lot less resistances
-the MV monster deals less damage
-the MV monster's attacks are about 10 points lower
So what have we learned from all this?
I'd say, based on this cursory analysis that if you want to port MV monsters into PF, you should do the following:
-as a rule of thumb, halve their Initiative score (but don't hold this as a golden rule)
-subtract ~10-12 from the monster's Defenses to get its Saving Throw values
-you should probably completely reroll all their Hit Points, as per the following formula [level+(level/4)]d8+Con bonus. This will NOT work universally, but it's a good rule of thumb.
-drop their damage output to 1/4 at first level and do the same with their attacks. 1/2 at second level and 3/4 at third. Leave it be at 4th. After that, add half their level to the original attack and damage. So if a lvl 1 MV monster does ~6dmg, drop it to ~3. If a level 3 monster attacks at +8 for ~10 damage, it now attacks at +6 for ~7 dmg. For a level 14 monster add +7 (14/2) to their attacks and damage.
That should about do it as far as math is concerned. But only playtesting can tell whether the powers and shticks can actually translate from one edition to another.