it's still all relative. htib's sound "good" in very very small rooms and only until you experience a real 5.1 and 7.1 system.
as a newbie awhile back, i was totally awed by the wonder of discreet channels when watching "the incredible hulk"'s "helicopter" scene with my samsung htz210 htib... and then i got to experience the same scene at my bestfriend's house when he had just installed his denon 1909- wharfedale 9.1 - 9cs - dfs and sub setup... my htib started sounding not as nice from that point onwards...
5.1 is still the standard that is safest to start with considering most if not all dvd's with dolby and dts are encoded up to 5 channels only. most receivers have algorythms that can turn a 5.1 signal into a 7.1, but most true 7.1 signals come from blurays with dts-hd and dolby true hd. also, most setups have a room that makes a 7.1 system unnecessary, as the rear surrounds are too close together rendering the rear left and right almost useless. HOWEVER, with a room at 40sqm, it has the potential to make the most of a 7.1 system considering its space...
If, aside from fighting games, you like playing FPS games on your PS3, a 5.1 or 7.1 ht system is a very very cool and useful experience... the first time i played COD4 online with my ht system, and someone shot at my character from his rear left, and i heard the shot from MY rear left, it made me smile quite a bit.
Just don't go into it blind. Audition as many systems as you like, to give you an idea of what you want. Just take into consideration that there will be wires involved in this 90percent of the time, so planning for that is, i would believe, also a priority.
And I'm just throwing this out there. You could also commission anthony/diy_master to handle the speakers. that would most probably lower your budget considerably without losing quality. i'm also sure mike c, avshop, SnS and/or Nemesis could cut you great deals if DIY speakers aren't your thing...
I have a 7.1 system, i use it for my HT, ps3 play, stereo music for jazz, classical, etc., and all 7channels for trance, house, sometimes RnB...
And Roy Focker rules!