We dont know when (if) the s800 will hit these shores. the s800 S4 is only being released because the s600/octa doesnt support LTE-Advanced, and naturally Samsung want to get in there with the LTE-A. Korea has been confirmed as the first and only region (so far) to get them (model numbers SHV-E330L,E330K,E330S). I would expect to see at least one network to have LTE-A up and running or to be close to doing so before we see a network release of the s800 S4. Currently none of the UK networks are even close. If this all happens in a reasonable timeframe and we see an s800 s4 here in the next year, say, then we might see the S800 but I would expect a price hike as well. If it takes longer than that for our networks to get LTE-A up and running, then we may well see the s4's successor first, which would probably make an s800 s4 release over here pointless.
Too early to get excited about.
As for wanting the fastest S4, should have got an i950
0?
I'd say replace the stock launcher with Nova. Other than that, just your usual suite of apps that you use, really, so FB/whatsapp or whatever. Use it for a week or so and decide if there's anything else about the phone that you dont like/want to change. Then you can start looking at custom roms and such. You could do that now of course but better to use the phone for a while before delving in. Plus, you know, warranty and stuff lol.
in other news, I've been using this icon theme with nova for a while now. I think it's excellent and minimal without being dull and monotonous. It also gets a lot of support from the Dev who's constantly adding new icons. Take a look
Stark Icon theme