Probably you are affected by performance regression since Opera 28, I have similar performance problems, lagging tabs when dragging, webpage scrolling lags or even halts when still loading and so on...
Best posts made by kroppy
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RE: Can't move tabs between windows in Dev 30Future releases
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RE: Keep #extended-lazy-session-loading flagSuggestions and feature requests
You close them before closing Opera.

No, simply no. Session is for a reason, which is to continue where you left off.
I don't see a point in loading tabs before activating them.
Where did Opera's policy go?
I mean what about traffic savings?
What about Opera Turbo, which is now gone from menu and is available only from options page?
I pay for each GB of traffic, so my suggestion is to give #extended-lazy-session-loading option back, or even put that functionality to options page as "Don't load tabs until selected".
Otherwise I'm forced to use another browser on my laptop. And I'm sure it's not only me. -
RE: Can't move tabs between windows in Dev 30Future releases
I cleaned up my entire profile and copied just bookmarks, cookies and passwords. I see improvements in tabs dragging and window refreshing
But scrolling is not much faster, especially on ZBCentral, Tumblr and Pinterest. What can be is that my HDD is heavily defragmented, even with my cache cleaned up, I hear my hdd when images load. Anyway what's most important I fixed my youtube problem, but I'm going off topic here 
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RE: dont load inactive tabsSuggestions and feature requests
Please add "Don't load tabs until selected" functionality to options page.