Is it just me or do you feel like LFR Ultraxion gives you much higher FPS than 25man heroic version of the same boss, even though most stuff should be pretty much equal in both modes? On our main raids i'm sometimes getting some very low FPS, especially at the pull, and it is just bearable at best, however in LFR this problem is almost non-existent.
Jokes aside I'm pretty sure your average LFR player will definitely have less button clicks per second than a heroic raider so I suppose that might make the difference on lag. I think a lot of it also comes from AoE heals being spammed on 25 people at once which is more or less absent in a lot of LFR.
i've noticed this too , but alas, this was before my old laptop died and i replaced it with a new one that can handle wow at a level i've never seen ( old one was oooooold :P )
one thing , throughout the previous lappy's life that i have noticed specifically for Ultrashion,. is to turn combat text off, this gains you a lot of fps( 5-15)se
Also the longer it takes to get the kill the more the boss will be casting Unstable Twilight thingy (the AoE pulse). At least good LFR groups can probably kill the boss faster than a 25HC guild.