This statement is very subjective but I went to verify myself how slow it really is:

Suppose a "quick website checking" involves initiating a search to find a potential website to enter and check (suppose you don't know site nor URL)

Typical example: input restaurant name + street + city in quicksearch, hit enter.

2.5G -> 11 seconds for results to show up after pressing enter key

3.5G -> 4-5 seconds

This is the time it can take the N900 to display my search results by instant search in MicroB, javascript disabled and cookies "ask first" , and non-javascript version of Duckduckgo, flash uninstalled.

(other conditions, 512MB swap, XMPP and Skype logged in, Mobile Vikings Internet, average quality reception, Nokia N900 showing only half or scale)

Next step is critical: as the time you spend waiting for a website to load depends heavily on the website. So you need your intuition to choose the website that is most likely to help you further instead of wasting your time by hiding information behind a "register now" wall and a lot of banners.

It is known that some websites use complex formatting that can bring down the whole N900 system to its knees for a while. But this is only when you expect it to run all the scripting and stuff.
If its just information checking you are after without logging on / off, your good w/o javascript and flash in 99% of the time.

It tried to bring my N900 down by opening as many various websites as I could and I received the yellow banner asking to close programs (to free RAM+ Swap) Once you have that condition, your N900 web browsing experience is likely to be less frustrating when it really counts.

Now we could finish and conclude that every website will load quicker on the latest octocore 3GB Android as in "instant access"

Luckily some progress has been made: capable web site programming and iPhone and Android phones become equipped with more powerful hardware, the mobile webworld seems no longer trending towards: "an iOS / Android app front for that web site" , a "mobile version" and "desktop versions" of web sites.

It seems that web developers have seen the light with some adaptive mobile friendly desktop websites. This starts to show in the big web sites first.
For example the browsing experience on Steam game fora or DPReview has vastly improved since 2009 on MicroB, actually providing a whole new experience for N900 users.

Nokia's web browser oriented approach combined with decent input devices (keyb, stylus, one finger zoom(!) ) seems to have been a right choice after all.

Of course the N900 lacks the processing power to offer a flawless experience to compete one on one with latest hardware when browsing on advanced scripted web sites and given the lack of updates security of the browser may be compromised.

But in many cases , when you want to actually do something with the data you find on the web: copy a telephone number, forward URL via IM, download and forward a file .. the N900 actually offers a very consistent experience regardless the weather.

I think by now you already start to notice that the Z3 is a few step forwards and a few steps back?