SE-NSE Forums:

Since the official 2.3.3 update for the X10 is out we can make a fair compare between the new and old flagship devices from Sony Ericsson.Day to day use:
After playing with the X10 a bit I have to say it isn’t smooth. Swiping between the screens has little lags which comes due its 32fps cap. What doesn’t make it better is that it doesn’t fully go up to the 32fps on 2.3.3 because on 2.1 it was smoother.
So in the point of smoothness the X10 loses against the Arc. The Arc scrolls smooth trough the screens, the app drawer and everything else. That’s because it is uncapped. It goes up to 60fps like all other uncapped devices.
The next point is opening apps:
Here the both competitors are both very good. They open the apps really fast, but again the Arc is faster, just a little but you notice it.
The only thing the X10 is faster is on opening the contacts and the messaging app, that’s because the X10 is clean, no contacts or texts on it. Just 5-8 apps.

Now we come to browsing:
And again both devices are very close. In loading pages they are both fast, but the Arc is a little bit faster. But pinch to zoom isn’t smooth on the X10 compared to the Arc, that may be because the X10 has buggy Dualtouch and the Arc has real Multitouch.
Both devices handle pages with flash quite well. I’d say it’s a tie here.

Last point is youtube, tested with the youtube app that comes shipped with them.
Both open the videos fast, but on the Arc it’s definitly faster. I’d say it’s a second faster, it was always noticeable.
Both devices were connected to the same Wi-Fi network.

Benchmarks:
Linpack:
Xperia Arc: 38.90mflops
Xperia X10: 36.322mflops

Quadrant:
Xperia Arc: 1683 (someone got 1790 points, also on stock ROM)
Xperia X10: 1322

Speedtest.net:
Xperia Arc: Ping: 87ms, Download 8.5Mbps, Upload 0.98Mbps
XPERIA X10: Ping 41ms, Dowload 7.2Mbps, Upload 0.98Mbps
These tests are from today. Xperia Arc scored a ping of 55ms and downlod of 12.3Mbps a while ago. My Wi-Fi seems a bit slow today.
But anyway, I’d say the Arc has faster Wi-Fi

Camera:
A lot of people want to know if the Exmor R sensor of the Arc makes a difference compared to the X10.
Here are some pics made at dark conditions:
X10:

Arc:

X10:

Arc:

I used auto mode on both devices to make the pics. As you can see the Exmor R sensor makes definitely a difference. So the Xperia Arc wins here, too.

We should keep in mind that the comparison was made right after the X10 got updated. So it’s totally clean (no texts, no syncing) and no apps are running and I only installed 5-8 apps for testing on it. That’s because it’s my spare phone.
The Arc is my daily phone and I have around 95 apps on it, a lot of texts, syncs emails etc, Facebook is on and push activated. Also it was up for 43 hours when I did the test.
So it’s a good achievement from the Arc. Clean and fresh restarted phones are faster than phones that run for a while and are loaded with apps.

As expected the Xperia Arc wins this dogfight but the XPERIA X10 isn’t bad, too. It’s a year older and you notice that.